Amazon would do (and probably still does) this in another way, too. When I was selling on Amazon for a bookstore, our strategy was try to find books that Amazon didn't have on the site, then sell them, and if any sold well we'd send massive quantities to Fulfillment By Amazon so we'd sell a lot and not have to ship each copy individually. The first time this happened, we sold something really well for 5 or 6 months, and then it stopped selling completely. Turns out Amazon started carrying it and was selling it far below list price. Then it happened again with another book after a few months of good sales. And then again. After the third or fourth time Amazon suddenly undercut us like that, we gave up on the practice, since between the already low FBA margins and the cost of returning all the unsold products to us (and the publisher) since we couldn't move them anymore, we weren't making enough for it to be worth the effort.