Buy or sell not buy and...
One party bought. The other didn’t. That’s against the terms because they used the transaction for that purpose.
Now if PayPal give his money back that would be great but having dealt with PayPal over the very same problem (albeit done on and not a gun) I can tell you the first thing they do is check the items against the terms. Luckily for the £2500 out of my pocket my item was covered. But they will try and wriggle as much as possible.
Tell you what, if you are so certain, cough for a small claim against PayPal should they not refund.