Simple automated bots taking lists of compromised logins and email addresses, and trying to log in to various sites with them. Then when they get a working login they already have a large list of the items they want to use, and scatter them around, figuring that 1% of the stuff might be bid on, and that 1% of that might be stupid enough to send email outside the walled garden, selecting the sheep to fleece. Then let them win the auction either for a low amount, using other compromised accounts to do the bidding up a little, and use the side channel to get payment plus shipping via some payment method that will not go via fleabay, and simply wait for the money. Then either send nothing, or send some fake tracking numbers, or send an epacket with something valued at $1 in it, using another legit seller to handle the order, and using their tracking info to pass it forward.
Low risk, reasonable return plus they also have valid email addresses that they know are both gullible and read by a human to sell on as well, and postal addresses to use for other scams as well.