I'm sharing this with you, NOT as a recommendation, but to show you how easy it has been for authors to manipulate the KU system, and believe me, many do it. Amazon needed to do something. A first warning would be reasonable.
I'm quoting from the internet here.
Ethan Gordon... product manager for www.BookYell(dot)com. BookYell is the greatest way to reach new readers to promote your KDP Select Enrolled Kindle Book and even get a guaranteed profit.
Unquote. Anything that promisesa guaranteed profit in this way is unethical.
Our promise is simple: we guarantee that your ..., will receive at least 75 Kindle Unlimited borrows within 48 hours ...you will earn a guaranteed share of the KDP Select monthly global fund. This makes us a unique and appealing service.
If Amazon traces you to using BookYell, or similar companies, you may get your account blocked.
BookYell is, of course, is only one small example. Much of the organised borrows is done within author groups.
If I go after crooks, (the systems, not the authors involved) I'm not going to be able to publish novels.
Scammers get shut down and come back looking twice as polished.