Social proof

When unsure, people look to what others have done and follow it.

Social influence Mainly on Product pages
Where it applies

Five of the eight page areas.

HomepageAlso applies CategoryAlso applies SearchNot typical ProductMainly here CartAlso applies CheckoutAlso applies Post-purchaseNot typical

Not usually a sitewide principle. See everything at work on Product pages

How to use it

Five ways to put it to work.

  • Show star ratings with the number of reviews, on product cards and product pages.
  • Include customer photos alongside written reviews.
  • Show recent negative reviews as well as positive ones.
  • Use “X bought this week” messages only when they come from real data.
  • Place testimonials near the call to action.
What the research found

Reviews move sales, in real sales data and two meta-analyses.

One-star reviews moved sales more than five-star ones.

Chevalier and Mayzlin found better reviews raised a book's relative sales on Amazon and Barnes & Noble, with one-star reviews moving sales more than five-star ones. Two meta-analyses found a modest positive link between online reviews and sales, but disagreed on whether review volume or average rating matters more.

Key research

Six sources, each checked.

Last reviewed

Chevalier & Mayzlin (2006) The Effect of Word of Mouth on Sales: Online Book Reviews J. Marketing Research Read the source Babić Rosario, Sotgiu, De Valck & Bijmolt (2016)Meta-analysis The Effect of Electronic Word of Mouth on Sales: A Meta-Analytic Review of Platform, Product, and Metric Factors J. Marketing Research Read the source Goldstein, Cialdini & Griskevicius (2008) A Room with a Viewpoint: Using Social Norms to Motivate Environmental Conservation in Hotels J. Consumer Research Read the source Cialdini (1984) Influence: How and Why People Agree to Things (New York: Morrow, 1984) Influence Read the source You, Vadakkepatt & Joshi (2015)Meta-analysis A Meta-Analysis of Electronic Word-of-Mouth Elasticity J. Marketing Read the source Bohner & Schlüter (2014) A Room with a Viewpoint Revisited: Descriptive Norms and Hotel Guests' Towel Reuse Behavior PLOS ONE Read the source
Before you use it · UK law

Fake reviews, reviews that hide an incentive, and presenting reviews in a misleading way (such as suppressing negative ones) are banned practices under the DMCC Act 2024, in force since 6 April 2025. Anyone publishing reviews must take reasonable steps to prevent and remove fake ones.

This is simply a pointer to check, not legal advice. Seek legal advice before you put this principle into action.