I'll give it 4 stars, no 5!

Cocktail party fact: the average rating for books sold on Amazon is about 4.1 stars out of a possible 5 stars. Aren't we all rather nice? For whatever reason, reviewers at BarnesAndNoble.com are even a little kinder—the average is 4.5 stars, and more than two-thirds of all reviews on the site are 5-star reviews.

David R. Bell, Location Is (Still) Everything: The Surprising Influence of the Real World on How We Search, Shop, and Sell in the Virtual One (Seattle: Amazon Publishing, 2014), p. 78