That sucks. I've been selling things on eBay for... longer than I care say out loud but I've read enough horror stories that I don't think I could get the nerve

That sucks. I've been selling things on eBay for... longer than I care say out loud but I've read enough horror stories that I don't think I could get the nerve to sell anything high-priced for fear that I would get scammed by a "professional buyer" like you did. They know eBay's rules and how to work within them to get what they want. Unfortunately, as a seller you have to know the rules as well as they do (or better) to keep the scam from working, and even that is not always a guarantee. When there is a dispute or request for a refund, as a seller, the hardest part is knowing the correction action to take when these things happen. If you do the wrong thing, or do the right things in the wrong order, you unknowingly paint yourself into a corner. You basically have to be your own "ebay rules lawyer" and read _all_ the docs and policies (some of which are hard to find) as well as discussion threads. One of the big things I do to defend myself against scammer buyers is I make it clear that I don't offer partial refunds, only full product returns where return shipping is (initially) at the buyer's expense and the shipping is reimbursed ONLY if the item is received by me in good condition. This isn't 100% protection against the kind of scam you encountered, but it's been effective for me so far.