Obviously, sales rank is important to Amazon. It makes sense to showcase products that are more likely to sell, and those that have been selling frequently have a proven track record. Sales rank factors into bestseller lists, ordering of search results (to some extent), visibility with special features, etc.

Sales rank is also important to authors and publishers. It helps to show how the book is selling.

Perhaps the strange thing is how important sales rank is to customers.

Popularity

Do people like to buy what’s popular? Aren’t there people with their own sense of style, who want something nice of their own that few other people are enjoying? Some clothes are highly popular, yet you still see a large percentage of people who are uniquely attired.

A few times in the past five years Amazon’s sales rank has been down for several hours to a few days. Sales tend…