Amazon allows 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. There’s not much recourse for authors when this happens, but some authors have had success in purchasing the inventory from the third-party seller in order to remove them as the primary seller, thus reverting the BUY BOX back to Amazon.