I can understand why little-known authors and their friends post reviews of their own books at amazon. Judy Chevalier has a paper that finds that good online reviews sell a surprising number of books. (A bad review suppresses sales even more than a good review boosts sales, which also makes sense.)
More puzzling to me is why everyday people post reviews.
Take the latest Harry Potter book, for instance. It has been out about a week. So far there are 1,385 reviews at amazon, and another 385 at bn.com.
What’s in it for reviewer 1,385? It’s not at all obvious. Perhaps reviewers in general want to influence what gets read. But it is hard to believe that one review has much impact in a pile of 1,385 of them, or even among the 295 reviews of Freakonomics at Amazon.
No doubt developing a reputation for being a top reviewer is a motivation for some people. Amazon obviously likes to encourage these kind of reviewers by giving frequent reviewers titles like “Top 1000 reviewer.” But this can’t be the motivation for most reviewers either.
Maybe it just feels good to write a review?
On the flip side, of course, most people who read a book don’t post a review. For the typical book, I estimate about 1 in 1,000 book purchasers posts a review at Amazon. So maybe I’m looking at it wrong: anytime only in 1,000 people does anything, the question can just as logically be posed as why so few people write reviews.