A theory on the ebay listing are that they are to catch bots on ebay and force them off the platform, possibly dropping prices for everyone by at least forcing the bot operators to spend time to bid on the various listing instead of writing/tweaking a bot to automatically attempt to buy any buy-now card or bid on any card below a certain value that they have set.
That is the theory at least. I still think some are scams trying to make a buck, but I don't see how given ebay's bias for buyers/purchasers.