As nobody else appears to have asked this.

When the buyer collected, is it on CCTV?

If it is, then that is unlikely to help with Ebay, but it will enable you to make a claim via small claims against the buyer.  You can also report to the police as they have effectively stolen the item.

And even if not, it might well be worth going down the route of sending them a "letter before action".

That might make them think twice about it.

And of course, if they are local, I would be tempted to get a mate to go along with me and turn up the the customers doorstep.
People get away with this kind of thing, because they are allowed to.
When it's not face to face, it's impersonal and they are just getting money off the machine, and not a real person.  Which makes it so much easier.