Do reviews increase sales? What the studies show

Why is it hard to know whether reviews raise your sales?

You have probably seen the numbers, such as reviews lifting conversions by a third or almost every purchase going to four-star products. Then you add a review widget, sales stay flat for a month, and you wonder whether any of it was true.

Part of the problem is where those numbers come from. We read the three vendor guides that rank for this question on 3 November 2026. Yotpo's guide, updated on 8 October 2026, says 100 reviews on a product can improve conversions by 37% or more, and the figure links to another vendor's blog rather than to a study. Trustindex's article on visitor trust gives its 70% figure from “our experience”. CusRev's guide to using reviews for conversion gives no figures at all. None of that makes the numbers false, but you cannot check them, and the companies quoting them sell review software, as we do.

The other part is cause and effect. Good products collect more reviews and also sell more, so a shop with many reviews selling well does not prove the reviews did the selling. The studies worth trusting are the ones designed around that problem.

What do the studies actually find?

We picked three studies that name their data, and read each one at its own page today.

Luca's study is the strongest of the three on cause and effect. Yelp shows each restaurant's average rounded, so two restaurants with almost the same underlying average can show different stars. Comparing restaurants just above and just below those rounding points separates the effect of the displayed rating from the quality of the food. Chevalier and Mayzlin used a similar trick with two shops selling the same books, so the book itself is held constant.

The Spiegel numbers are the ones you see quoted most, often without the name. They are useful for shape rather than size. The first handful of reviews matter most, and a near-perfect average does worse than a good one. The center's page also reports that displaying reviews raised conversion more for a higher-priced product than for a cheaper one, by 380% against 190%, but the chart on the same page gives slightly different figures, and the method is not published there. Treat the exact percentages with care.

When do reviews matter most?

Reviews matter most when the buyer has little else to go on. Luca found the whole effect in independent restaurants and none in chains, and his reading is that online reviews stand in for the reputation a chain already has. The same logic applies to a small online shop, where a visitor who has never heard of you leans on other customers far more than one who buys from you every month.

Price seems to push the same way, judging by the Spiegel center's larger gain on the dearer product. And the first reviews do far more than the hundredth. Going from none to five changes how a product page reads; going from 95 to 100 does not. If you have none yet, our guide to getting your first reviews is a better use of your time than polishing the widget.

Do bad reviews hurt more than good ones help?

Yes, one bad review weighs more than one good one, but a page with no bad reviews at all is not the goal. Chevalier and Mayzlin found that a 1-star review moved book sales more than a 5-star review. The Spiegel center found purchase likelihood falling as the average climbs from about 4.7 towards 5.0, which suggests buyers trust a perfect score less.

Put together, the practical answer is to keep the honest mix and reply to the complaints. A shop with a 4.6 average and visible replies looks real; a wall of five stars looks curated. Our article on the benefits of negative reviews goes into how buyers read them, and the one on responding to negative reviews has replies you can adapt.

What can our own data tell you?

Very little about sales, and we would rather say so than invent a number. Formgong counts reviews, not orders, so we cannot see whether a shop sold more after its reviews went up. We looked anyway, reading our production database on 3 November 2026 without changing anything. Seven sites on Formgong had approved reviews that day. One of them belongs to an outside account and has 2. The other six are our own test and demo sites, with 146 approved reviews between them, 101 of which we imported ourselves from files. That is not a sample anyone should draw conclusions from, and it says nothing about revenue.

What you can do is measure your own shop. Pick a few products that have no reviews, ask their recent buyers, and compare each product's conversion rate in the weeks before and after it reaches five reviews, in the same season and with no price change. It is not a controlled study, but it is your data, and it answers the question for your shop rather than for restaurants in Washington State. Our guide to getting more customer reviews covers the asking part.

How do you get the effect without faking it?

Show real reviews where the decision happens, on the product page next to the price and as a short store-wide row on your homepage. Label reviews from people who actually bought, because the Spiegel center reports that a verified-buyer badge raised the odds of purchase by 15%. And keep the lower ratings visible, since the studies above suggest that a believable average sells better than a perfect one.

Formgong's review widget is built around that last point. It has no setting that drops low ratings from the list or the average, its count is labelled “approved reviews” so it never passes for every review received, and reviews that came through an order link carry a “Verified buyer” mark. Trustindex's homepage slider page, read on 3 November 2026, lists “Hide your negative reviews” among its features; we chose not to build that. The review widget page shows how it looks and what each plan includes.

Have reviews changed your sales?

If you have numbers from your own shop, before and after reviews, we would like to see them, even if they show no change. Write to support@formgong.com. With your permission we will add them here.