Influence: The Psychology of Persuasion

by Robert B. Cialdini

The more stars assigned to a product, the higher is the likelihood of purchase—but only up to a point. When the average rating moves past the optimal 4.2 to 4.7 range, purchasers become suspicious that the ratings are phony and are less likely to buy. Negative reviews establish credibility. Consistent with the Center’s contention that near-perfect ratings undermine trustworthiness, the presence of a negative review adds credibility to product evaluations. In fact, if a site includes some negative reviews, the conversion rate jumps by 67 percent. Verified buyers are gold as reviewers. Verified buyers, who have been confirmed to be previous online purchasers (rather than paid reviewers), are viewed as more credible. Accordingly, their presence on a site increases sales measurably.