Why all 5-star reviews are bad news

Aside from my feeling that a star system is much too crude a measure to evaluate books (or restaurants or coffee pots or airlines or most products and services), they have another

What you want to see for your book.

deficiency: too many good ones can deter prospective buyers.

As Tom Collinger, a Crunch Network contributor, writes in Tech Crunch, "when consumers see only five-star reviews, they smell something fishy, something that causes their BS meter to go off. They know that some negative opinions about a product, service or place are to be expected, and become suspicious when something is marketed as 'perfect.'"

Collinger cited a Northwestern University’s Spiegel Research Center and PowerReviews study of 40 product categories that looked at the impact of reviews on purchases. In moderation, bad reviews actually help boost sales—"product purchases were most influenced by reviews with an average star rating between 4.2 and 4.5."

Amazon says that it "calculates a product’s star ratings using a machine learned model instead of a raw data average. The machine learned model takes into account factors including: the age of a review, helpfulness votes by customers and whether the reviews are from verified purchases." I'm not sure what this means because when I post a review, the site asks me to assign a star to the book.

In any event, this means don't tell all the friends you inveigle into reading your book to give it a five-star review. You want a mix of five-, four-. and even one or two three-star reviews. Better yet, you want a thoughtful, appreciative comment.