I agree, crich. The real issue is the reviewer's relationship to the author, not the reviewer's profession, and Amazon has no way of policing that unless the reviewer states it overtly. Enemies and stalkers write negative reviews for reasons that have nothing to do with commerce, and everyone has friends and family who write reviews in an effort to show support.
The advantage of an author's review is not that they'll necessary like one's book but that they might have a better sense of what one is actually doing. Effectively Amazon is disallowing reviews by some of the very experts whom book review digests court.
However, if you apply this policy to commercial products made by companies, and are disallowing employees from writing product reviews, then the idea makes far more sense. I wonder whether Amazon has simply made an unfortunate transposition of a policy which has yielded positive results elsewhere -- one which does work when applied to a corrupt dynamic which is easier to trace.
Fraudulent reviews often occur around health products with questionable claims, and those do have to potential to harm the customer. Yerba mate, agave, kombucha -- all have markets which depend on the suppression of knowledge about side effects and the repetition of claims which various studies have discredited.
I've noticed that companies often combat discouraging data by spamming venues with arbitrary posts by a succession of supposedly disinterested users -- posts which share the same phrases, contain the same mistakes in grammar and spelling, and are in the same style.
This doesn't just happen on Amazon. It also happens on health and science blogs. You can also find the same equivocations and tap-dancing at Wikipedia's back end, where the validity of facts and conclusions in Wikipedia articles is being discussed.
It's the reason that research on health issues can look far more favorable on Wikipedia than elsewhere.
Last edited by Prestidigitweeze; 01-23-2013 at 04:58 AM.