The book publishing trust system was based on the ISBN. Every book should have had an ISBN, it was not given to everyone in a row. With the advent of the open market of electronic books, this order was violated.
In every complex ecosystem there are parasites
(c) . Sooner or later spammers and fraudsters get into any open system of communications, such are the laws of nature. Therefore, it is quite natural that the growing popularity of e-books attracts more and more different rabble (moneymakers).
Moneymakers from book publishing have two main types of “business”. The first is garbage content generation. This can be automatic content generation, theft of network content, for example, from Wikipedia, etc., semi-automatic aggregation of content from open sources, export of everything collected in the book format and sale on Amazon and other sites (the scheme is accompanied by the creation of many fake accounts and writing favorable reviews).

Some
authors have already crossed the milestone of 3,000 published books and continue to create, selling including texts in the public domain after the expiration of copyright.
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The
screenshot shows something called Autopilot Kindle Cash for teaching people how to generate dozens of books a day and publish them on Amazon.

The second scheme is the theft of someone else's book. Someone is engaged in scanning paper books and selling electronic versions, even without having a copyright on the book itself. Here we are talking about books that exist only in paper form and have not yet come out in digital form (there are actually a lot of them), or about the issue of cheaper copies of existing electronic publications.
It seems that soon online stores will have to turn to search engines for advice on how to deal with content farms. Probably, you can use text analysis systems for plagiarism, more competent reputation systems for authors and publishers.