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Customer Research Methods: 4 Public Sources Plus Ads, Tested

By Daniel Derzic, founder of Adlicio · Oct 30, 2026 · 14 min read

On this page

• What we found
• Four public sources, one product: what each one found
• How many comments are enough?
• How much of each source is usable?
• Before you post a survey on Reddit
• The other customer research methods, in brief
• How to choose a method
• How we got this data
• FAQ

The main customer research methods are interviews, surveys, focus groups, usability tests and desk research, which means reading what buyers already wrote in comments, reviews and ads. We tested the desk methods on one product: 1,727 Reddit, YouTube, TikTok and Amazon comments and reviews about magnesium glycinate, plus the competitor ads running that week. Every item was coded against one list of 55 pains, objections and hoped-for outcomes, so we could count what each source found.

What we found

• ✓All four sources found mostly the same worries and hopes: 41 to 52 of the 55 themes each.
• ✓The wording barely overlaps: only 2 of 409 vivid phrases appeared in more than one source.
• ✓Low-star Amazon reviews were mostly about the bottle that arrived (89.3%), a theme comments almost never raised.
• ✓About 220 comments found 90% of the themes; the rare ones took hundreds more comments each.
• ✓The share of negative comments ran from 8.1% to 55.9% across Reddit threads, wider than between platforms.
• ✓20 of the 30 large buyer and founder subreddits restrict survey or research posts; reading threads needs no post.

Four public sources, one product: what each one found

These are observational, or desk, methods: reading what buyers already wrote. We did not test interviews, surveys, focus groups or usability tests. Comments are not evidence that magnesium glycinate works; they show what buyers say, worry about and hope for.

The four sources found largely the same themes, 41 to 52 of 55 each. TikTok was the fastest read per theme and the most vivid, but it missed 14 themes, mostly specific health complaints such as cramps and restless legs. So one well-chosen source finds most of what buyers worry about.

Same themes, different words

29 of the 55 themes appear in all four sources, 23 in three, 2 in two and 1 in only one. Any two sources share between 61% (TikTok and Amazon) and 87% (Reddit and YouTube) of the themes the pair found.

Of the 409 distinct vivid phrases the coder marked (slang, idiom, metaphor or exaggeration), only 2 appear word for word in more than one source: "up all night" and "works like a charm". For a copywriter, a second source adds wording far more than it adds themes.

Reddit: objections and side-effect stories

Reddit had the most objection mentions, 90.4 per 100 comments. Its top themes were worse sleep (12% of comments), better sleep (12%), dose or timing (9%), "works for some, not me" (9%) and no effect (8%).

"Magnesium glycinate works for a lot of women, but not for me. Around 2 or 3 AM I was wired and ready to run a marathon. I no longer take it at bedtime." (r/Menopause)

Reddit's 60 "fake or poor quality" mentions sit mostly in two r/Fitness_India threads and are about honest labeling:

"Turns out all the brand promising 22% glycinate are buffering with magnesium oxide" (r/Fitness_India)

YouTube: how and when to take it, and older buyers

One in five YouTube comments (20%) was about how much to take and when, the largest single theme in any comment source. YouTube also produced the only theme no other source raised: age-related concern from older buyers, in 6% of comments. If your buyers skew older, start with YouTube comment analysis for ads.

"I made all mistakes you talked about in this video [...] Comments from a 72 years old senior." (YouTube)

TikTok: dreams and quotable verdicts

TikTok comments ran a median of 10 words. The top theme was vivid dreams (12%), then dose or timing (10%).

"magnesium literally makes me have the MOST vivid dreams. they're are BEYOND intense." (TikTok)

"She finna be sleep for 40 days and 40 nights" (TikTok)

Lines like these already work as openers, the idea behind turning TikTok comments into ad hooks.

Amazon: outcomes up top, the bottle at the bottom

We pulled 229 reviews of the top-selling magnesium glycinate listing on Amazon (4.7 stars, 51,842 ratings) and oversampled low stars on purpose: 122 are 1 to 3 stars, while 1-star ratings are 3% of the listing's published histogram.

The 4 and 5 star reviews (n = 107) are outcomes: better sleep in 50%, calm in 28%, easy on the stomach in 24%.

"From the first night I took it, I felt this incredible sense of calm wash over me like a gentle wave, and I actually slept through the night without tossing and turning." (Amazon, 5 stars)

The 1 to 3 star reviews (n = 122) are mostly about the bottle that arrived: 109 of them (89.3%) describe a packaging, damaged-seal, quality-control, returns or delivery problem, against 6 of the 107 high-star reviews (5.6%). A keyword check for words such as seal, broken and damaged agrees: it hit 74 of the 122 low-star reviews (60.7%), 8 of the 107 high-star reviews (7.5%) and 3 of 1,498 comments, only 1 of them about packaging, so comments almost never raise it. On Amazon, 34 of the 42 "fake or poor quality" mentions carry a packaging or quality-control note. Read this as what low-star reviews discuss, not how often the product fails.

"when I opened my new bottle noticed my fingers had white powder, I poured more capsules out and found an open one empty. Don't feel confident about this batch" (Amazon, 1 star)

"Order picked by someone who just changed their oil" (title) "The bottle is disgustingly dirty." (Amazon, 1 star)

This theme makes the case for mining Amazon reviews for ad angles one star band at a time.

What competitor ads already say

The first 30 live US Meta ads for "magnesium glycinate" came down to 7 unique copies from 4 advertisers. Four lean on the form and absorption, four on purity, and three each on calm and sleep. That is a map of crowded claims, not customer voice.

How many comments are enough?

For interviews, Guest, Bunce and Johnson saw new themes stop appearing within the first 12 of 60 interviews (Field Methods, 2006). Hennink, Kaiser and Marconi had "heard it all" by interview 9 of 25 but needed 16 to 24 to "understand it all" (Qualitative Health Research, 2017). For open-ended surveys, Marvin's guide plans 20 to 100 or more responses and gives no source. Our count, four sources pooled:

About 220 comments (median 219, range 131 to 407) found 90% of the themes, and all 55 took a median 614. After the 90% point, each new theme cost a median 276 more comments. Against Marvin's range, 25 comments found about 20 of the 55 themes and 100 found about 41; survey answers are prompted and comments are not, so the comparison is rough.

Per source, each measured against its own total (which flatters small sources), 90% of the themes came at 140 Amazon reviews, 162 TikTok comments, 196 YouTube comments and 232 Reddit comments. After that point Reddit needed 109 more comments per new theme, the others 19 to 34.

By thread, across the 16 threads and videos, 1 gave a median 24 of the 55 themes, 3 gave 46, 5 gave 51 and 8 gave 55 (range 51 to 55).

Common themes came first (better sleep at comment 6). The last were rare: blood sugar (median first appearance at comment 246), low mood as the reason to buy (244), fear of dependence (230) and constipation (224).

"I'm just scared to start then when I'm off of it it worsens" (TikTok)

The count cannot see what the list missed: 218 of the 1,727 items gave an opinion that fit none of the 55 themes, 124 of them with a specific point (79 on Amazon). Our rule of thumb, from one product and one coder: read about 220 comments across 5 to 8 threads or videos, then hunt for the rare themes on purpose.

How much of each source is usable?

Attest's guide warns that people "are often more vocal about complaints than positive experiences". Our sample does not settle that. It shows the thread you open moves the negative share more than the platform. On Reddit alone the negative share ran from 8.1% of comments in an r/Fitness_India brand thread (n = 123) to 55.9% in an r/Supplements thread titled "Magnesium Glycinate was the worst thing ever." (n = 118). Another r/Supplements thread, "I finally understand why everyone won't shut up about magnesium glycinate", came in at 13.3%. Open threads with different framings before you judge sentiment.

About a third of YouTube comments (31.5%) were off-topic: praise for the creator, jokes and spam, such as "this is the best Doctor online!" (YouTube). Among comments that state a view, 47.0% were negative on Reddit (n = 489), 49.6% on TikTok (n = 139) and 28.7% on YouTube (n = 115).

Amazon gets no sentiment share, because we pulled reviews by star. Its published histogram (84% 5-star, 9% 4-star, 3% 3-star, 1% 2-star and 3% 1-star, of 51,842 ratings) matches the J-shaped distribution Hu, Pavlou and Zhang described: "mostly 5-star ratings, some 1-star ratings, and hardly any ratings in between", driven by who buys a product and who bothers to review it (Communications of the ACM, 2009).

Before you post a survey on Reddit

An r/smallbusiness poster wrote in September 2026: "almost every community where those customers actually are has an explicit rule against posting to validate an idea" (thread). 20 of the 30 large buyer and founder subreddits we checked restrict survey or research posts: 14 outright and 6 only with mod approval or in a set thread. 8 ban only self-promotion or soliciting, and 2 had no relevant rule. The 20 hold 75.1% of the 80.5 million subscribers covered. By niche: parenting 5 of 5, skincare 5 of 5, fitness 4 of 5, small business and e-commerce 4 of 5, SaaS and startups 2 of 5, supplements and health 0 of 5.

"please don't use this group for surveys or consumer research." (r/30PlusSkinCare rules)

"Please do not conduct market research on our community. We are not your focus group" (r/smallbusiness moderator reminder)

That contradicts a common tip: Dovetail's guide says "Forums, advertising, local groups, and organizations are good ways to identify potential customers to participate". These rules cover posting, not reading, and none of them endorses data collection. The route that needs no post is finding pain points in existing Reddit threads, which is how this study worked.

The other customer research methods, in brief

The ranking guides, including those titled market research methods, share one core list but disagree on whether public comments are primary or secondary research.

• ✓Interviews get the story behind the last purchase.
• ✓Surveys measure how common an answer is.
• ✓Focus groups show group reactions, which loud voices can steer.
• ✓Usability and prototype tests show whether people can use a page or product.
• ✓Analytics and A/B tests show what people do, not what they say.
• ✓Observation and field studies watch behavior where it happens.
• ✓Competitor analysis maps what rivals offer and claim.
• ✓Social listening and review mining read unprompted public talk, as measured above.

Most also share a process: set an objective, pick a method, collect, analyze and act, and use more than one method. To match software to each method, see our comparison of customer research tools.

How to choose a method

Start from the question. "What do buyers worry about, and in what words?" calls for desk methods first.

"Will they pay this price?" calls for a survey or a pricing test, "Can they use it?" for a usability test, and "Why did they buy, or leave?" for interviews, ideally after the desk pass.

With the objections in hand, the next job is pulling objections into ad messaging.

How we got this data

One product, magnesium glycinate. Comments collected 2026-09-23, Amazon reviews 2026-09-24.

• ✓820 Reddit comments with replies from the 7 most-commented threads of the last 24 months with "magnesium glycinate" in the title (3 r/Supplements, 2 r/Menopause, 2 r/Fitness_India), dated 2025-02-18 to 2026-09-22, minus 25 deleted and 3 bot comments.
• ✓400 top-level YouTube comments, 100 per video by relevance, from the 4 most-viewed English videos with "magnesium glycinate" in the title, brand ads excluded, dated 2023-09-22 to 2026-09-23.
• ✓278 TikTok comments, about 60 per video, from the 5 most-liked videos of the last 24 months with "magnesium" in the caption, dated 2026-02-27 to 2026-09-23.
• ✓229 Amazon reviews of one listing, Pure Encapsulations Magnesium (Glycinate), 90 capsules: 99 five-star, 8 four-star, 9 three-star, 14 two-star and 99 one-star. 118 are dated, 2019-03-17 to 2026-09-20.
• ✓The first 30 active US Meta ads for "magnesium glycinate" on 2026-09-23: 9 for the product, 8 with body text.
• ✓Posting rules of 30 subreddits in six niches, 2026-09-23: the top 5 by subscribers from 7 candidates per niche listed before any rules were pulled (an editorial pick), coded against a rubric fixed in advance.

The 55 themes (17 pains, 22 objections and 16 desired outcomes) come from a codebook drafted on a 170-item sample of all four sources and locked before the full pass. Coding was LLM-assisted: one model read every item and assigned a class, codes and at most one vivid phrase of 2 to 10 words. A second, blind model instance, not a human, checked random samples and agreed on the class of 46 of 50 items (Cohen's kappa 0.90) and 35 of 40 Amazon reviews (kappa 0.80). Reading time is words divided by 238 words per minute, the adult silent reading rate for English non-fiction in Brysbaert (2019).

The random-229 row averages 200 random draws per source, so sources of different sizes compare fairly. Overlap is measured at this 55-code grain: pairwise Jaccard similarity (shared codes divided by all codes the pair found) runs from 0.61 to 0.87, and content-word overlap between the vivid-phrase lists is 0.05 to 0.17. The comment count measures code saturation, when a theme first appears, not when it is understood. We shuffled the 1,589 rows not used to draft the codebook 50 times.

Limits: one product and one coder. Two Reddit threads come from an Indian fitness community. The codebook sample's Amazon items were Amazon's own featured reviews, mostly five-star, so it had no packaging code; the packaging figures come from coder notes that were not second-coded and from a keyword rule for physical-condition words, a proxy. Some YouTube and TikTok comments may be promotional. Quotes skip comments that disclose diagnoses or medicines.

Adlicio, our product, pulled the Amazon reviews. It is built for voice of customer research and pulls verbatim customer comments and reviews from public sources (Reddit, Amazon, YouTube, TikTok, Instagram, Trustpilot, G2, App Store and more) and groups them into pains, objections, desired outcomes and phrases for ad angles.

FAQ

What are the 7 basic research methods?

No ranking guide gives a fixed seven. A practical seven for customer work: surveys, interviews, focus groups, usability tests, observation, analytics and experiments, and desk research such as reviews and comments.

What are the four types of research methods?

Marketing guides usually answer primary, secondary, qualitative and quantitative. In research-design terms the four are descriptive, correlational, quasi-experimental and experimental.

Can you give me an example of customer research?

This page is one: 1,727 public comments and reviews about magnesium glycinate, sorted into 55 pains, objections and hoped-for outcomes.

How many reviews or comments do I need to read?

For one product, about 220 comments found 90% of a fixed 55-theme list, and 5 to 8 threads or videos found nearly all of it.

Can I post a survey on Reddit for market research?

Usually not in large communities: 20 of the 30 we checked restrict it. Reading existing threads needs no post.

Pick one product question, open five to eight threads or videos with different framings, and code about 220 comments against a fixed list before you write a single survey question.