Good question.
I have thought that since the payments are called an “advance”, that these are payments to be netted against the actual sales of the books, and will be netted against whatever royalties are due to the author, when they settle up accounts when actual sales roll in.
And, in the case of a book that doesn’t sell, conceivably the author could owe money back to the publisher, since it was an “advance”, not an actual specified contractual amount of an owed payment to the author.
Are these payments really advances; does an author of a dud like this Cuomo book get to keep the money paid as an advance?
It's also necessary to police bulk sales to political groups that are also laundered bribes.