Dave, even though this is an online sale. It's based on the same principles as if it were a retail space on the high street. If they wish for a refund, then they must return the goods first in doing so. I've had similar issues with buyers damaging the goods, swapping parts out and not sending the goods at all. So you live and learn, but no goods, no refund. Advise them of the terms and conditions of T.M. Sellers do have rights also. ;)