If emails from Amazon's customer service team are a fair indicator, it appears the online retailer considers authors to be direct competitors of other authors. And email chains are all we have to go on, as Amazon did not respond to our request for comment.

On Wednesday, Steve Weddle, an author of crime fiction, blogged about how he had tried repeatedly to leave a nice review for "Karma Backlash," a pulpy e-book by his friend Chad Rohrbacher, on its sales page on Amazon. Weddle's review was received but never posted.
When he asked Amazon what was happening, Weddle got this an email reply that explained, "We have removed your review from Karma Backlash. We do not allow reviews on behalf of a person or company with a financial interest in the product or a directly competing product. This includes authors, artists, publishers, manufacturers, or third-party merchants selling the product. As a result, we've removed your reviews for this title."

It is certainly possible that some authors consider other writers rivals. In September, prize-winning English crime writer R.J. Ellory admitted to having written negative reviews of other writers' books under a pseudonym. The furor that erupted over his "sock puppet" reviews, however, was just as heated around the positive pseudonymous reviews Ellory had written,. which were for his own books. Ellory, who has since apologized, called one of his own books "a modern masterpiece."

This is the conundrum of reviews on Amazon: For the most part, they're not actually reviews. In terms of books, they're often reactions, thoughts, comments, recommendations -- but not book reviews in the classic sense. Book reviewers are supposed to steer clear of work by friends and enemies. That kind of thing has never been the rule at Amazon.
More at LA Times