There was an author named David Vise who bought a garage full of his own book and then later returned them that first tipped off the NYT that people were seriously gaming the ratings.
They want books in the bestseller list that people actually are buying to read, not just as a way to backdoor a political contribution.
I think Congressman Jim Wright had a scandal with the same sort of nonsense.
I actually saw a copy of Jim Wright’s book in an elementary school office one time. Some pages had one sentence and others were blank. Total scam.