An anonymous author writes about buying positive Amazon.com reviews for their book on Fiverr.

Eight hours later, I checked my ebook’s page on Amazon and there it was: A glowing, five-star review! Four paragraphs in length, even. And it appeared the reviewer had actually read my ebook. “A one-of-a-kind vampire book!” read the subject line. The reviewer name-dropped several top vampire television shows and movies in the review (Twilight, the Vampire Diaries), a nice touch (and one that would, of course, help my ebook out when Google’s search engine spidered the Amazon page). Through several details in the review, it was apparent that the reviewer had actually read my book. Or at least skimmed it. It sounded like a lot of work to go through for just five bucks. Or four bucks, since the reviewer spent .99 to buy my ebook, thereby giving it a quick sales ranking boost.

I clicked on the reviewer’s name and saw a list of dozens of other five-star reviews that they had written. Every book was self-published, and every book was rated five stars. I recognized one of the authors on the list as a self-published writer whose ebooks regularly hit the Kindle charts’ Top 100. “You need a critical mass of readers to generate word of mouth,” the author wrote in a guest post on a popular “indie publishing” blog. Word of mouth, or a critical mass of fake reviews and purchases to push your ebooks into the Kindle Top 100? With ebooks, visibility is a big part of the marketing equation. Once an ebook hits the Kindle Top 100, sales tend to snowball as new customers discover it in greater numbers.

I'm not saying that online reviews are all untrustworthy, but I am saying that you shouldn't use them as your primary source, unless you're willing to investigate the history of the reviewer.