In the first year of Kindle Unlimited, scammers took advantage of the system by uploading ebooks so short that they got paid after only a few pages were read. Amazon put a stop to that in July 2015 by switching to a system that paid based on pages read, and in response the scammers invented the book-stuffing con and started uploading really long books.
The way that the book-stuffing con works is that scammers stuff lots of extra content into an ebook before uploading it to Kindle Unlimited, and then trick readers into jumping to the end of the book.
Thanks to a flaw in the Kindle platform, namely that the platform knows your location in a book but not how many pages you have actually read, the scammers can get paid for a user having "read" a book in Kindle Unlimited by getting the user to jump to the last page.
https://techcrunch.com/2018/06/11/notor ... bookstore/
Carter and his books are gone but books stuffers like him still exist. While it’s not a crime per se, it does muddy the Kindle ebook waters and brings garbage content into the market. While most of us wouldn’t fall for these cynical tricks, plenty will and that makes it a danger to readers and a boon to scammers.