They got rid of categories for books a couple months ago. Most books are listed by mega dropshippers, and they are all BIN. So are most storeholders', because it costs 5c a month to list BIN in a store and $1.50 for a max of 10 days to auction.
And unless they are highly collectible, most book auctions don't seem to get close to what they're worth. I certainly won't risk auctions.
