You buy something off eBay
Item arrives in Amazon Box + Amazon 'Gift' Invoice - so seller is obviously just an Amazon Droppshipping Account.
You request refund and seller is super helpful (through eBay Messaging).
Returns Case is opened and eBay give you the option to Print Return Label (which would be an eBay Label addressed to the sellers address).
Seller then contacts you (directly, not through eBay Messaging) and gives you the Amazon Return label for a "speedier refund" or something along those lines.
You send the item back (via Amazon Return Label).
Wait X days and contact seller asking for the refund.
They automatically close the case (selecting something like "We Cant Sort This Out" and request eBay to step in).
eBay can see from their label tracking, that the item hasnt been returned so automatically close the case and favour with the seller.
You cant open another case, so you're out the item and however much you paid for it.
Also, if you lose a case, it automatically removes any associated feedback and locks you out leaving any if you hadnt by this point... So according to the sellers feedback account - nobody will ever know!
I just fell for it with a £30 item, but I rang eBay and complained and because I buy and sell quite a chunk, they just gave me a refund. This wouldnt have come out the sellers pocket though, so they've got away with it still.