The truth is that gaming Amazon's system is the norm. I've even experienced the work of Amazon gamers. One "reviewer" left a negative review on one of my books, only to recommend another book they said was better. (I became suspicious because the recommended book was on an entirely different subject.) After some research I discovered that these reviews had appeared verbatim on other books in the same category as mine. It was obvious that the "reviewer" was paid. (I reported the incident to Amazon. Nothing happened.) There are also fake reviews generated for political purposes, such as the thousands of "reviews" of Hillary Clinton's new book which Amazon was recently forced to delete.
At the moment, Amazon is suing over the ways their current payment system for KDP is being gamed. The new system is based on pages read, rather than downloads, because services were downloading books for a fee in order to boost a book's ranking. But the new system hasn't made a dent in the abuse. Thu-Huong Ha, writing for Quartz, has described in vivid detail some of the tricks being employed.
1) Inflating pages read. How can Amazon determine the number of pages a person has read of an ebook? Simple. Reading devices do not record the pages you read sequentially. Therefore, if someone is on the first page, and then jumps to the last page, the device will record the whole book as read. Who would want to read only two pages? Well, nobody. But if on the first page there is a "free offer" of something on the last page - voila! These books can even be composed of complete nonsense, and there will still be a payout.
2) Authors can create fake accounts, or hire a service that owns numerous accounts, to download massive numbers of books on free days. The author earns nothing, but the book will appear on Amazon's bestseller list for free books, which will enhance its attractiveness to future buyers.
3) Fake reviews. This has been a problem from the start. An author or company can buy fake reviews on Fiverr for a few bucks. Authors and companies can also purchase negative reviews of similar products (that's what happened to me) in order to drive down the ratings of the competition. Amazon has become so paranoid about fake reviews that it will remove a review from anyone even vaguely connected to the author - a Facebook friend, for example, whom the author may never have met.
The bottom line on Amazon rankings is that the system will always be gamed. It doesn't matter how many people Amazon sues, or how many new contortions it introduces into KDP, there will always be some way to work around it.
It makes you long for the old days, when all you had to do to get bestseller status was either sleep with a reviewer for the New York Times, or give birth to one. Ah, things were so much simpler then.