Basically, Amazon is now allowing third-party sellers to compete for the BUY buttons for books in new condition. This means that, even though we have inventory available of your book with Amazon, there’s a chance Amazon will retain the BUY button and allow third-party sellers to bid on it, allowing that seller’s site pops up as the main “seller” when you go to your Amazon page. Apparently it’s been a common practice for other Amazon categories for some time, and has no been extended to books.