As it turns out, many of those who seem to be extolling the virtues of that e-book you're considering do not actually exist. They never bought the book about losing weight in ten days or learning Spanish in a week. It's all made up, figments in the ether, and you, the fool, will soon be parted from your money.
The paid reviews that dot Amazon are hurting small publishers and self-publishers, who are doing things the old-fashioned way. Free books are given away in the hopes that the recipients will take the time to post a real review and generate sales through the little buzz that can be created. It costs money, but you can't get the reading public's attention without investing in promotion.
Like any other money-making venture, there are those who find a way to game the system and skirt the rules. Those who cheat hurt the honest majority. Just ask anyone who has seen their legitimate positive reviews pulled from Amazon because the Amazon review metric determined the review was not legitimate.
It comes as no surprise that Jeff Bezos sent one of his investigative reporting teams to probe deeper into the swamp. A man buys the Washington Post to get something back out of it, after all, so why not examine the seamy underside of Amazon's Kindle Direct Publishing.
The reporters found that the faux reviews are used extensively by a few entrepreneurs who are slapping shite together and calling it a book, publishing it through Amazon, and then buying enough good reviews to move the drivel up the charts so it shows up at the beginning of a search for the topic of interest. A reader looking for such a book reads the glowing reports, and makes a purchase they will later discover was not at all what they thought they were getting.
Pseudonyms are used and false identities created to lend an air of authority, the entire scheme devised to trick readers into buying an unknown quantity, trusting the seller to be honest. When the book turns out to be worthless, the reader fires off a scathing review of their own, but for small sums of money they aren't likely to go to all the trouble of demanding their money back. And what becomes of the real reviews? The scam artist complains to Amazon about abuse and Amazon takes those reviews down.
Amazon makes money off the transaction, of course, and would not have a strong incentive to stop the practice. What drives Amazon to block the paid review resides in long-term strategy. If, over time, readers come to see Amazon's Kindle publishing arm as a vast carnival game skewed against them, they won't consider Amazon-published e-books. The model will fall apart as the leeches suck the life out of it with the lie of the false review and the fake author, and the money machine shuts down.
When it comes to e-books, you're safest with fiction because it's all made up. There are no experts to be trusted, just authors with a talent for telling stories. They'll let you sample the opening of the book, the digital equivalent of thumbing the pages in a bookstore. It's about the closest you can come to actually seeing what it is you're buying before buying.