The way they're doing it doesn't make sense and is poorly implemented. a MUCH better way would have been to sell ads on the post order page, or thank you page. For example, if you bought a book on "bigfoot", then I could buy a spot on that thank you page as "Other books similar to this you might like". I'd gladly pay for that. But they are burying the ad the way they're doing it now and it won't be effective.