Look for employment clues...
I had a remarkably quick resolution to a similar ebay issue when after a lot of email and calls to the other party I called the company that he worked for, who's contact details had been used for either ebay or paypal (I can't remember which) and asked the personnel department if they could confirm he worked there.
I explained I needed to know as I expected in the near future to be forced to serve an injunction to stop the running of the ebay business connected to thier business premises.
They took a few details... that evening he got in touch and resolved the problem.
May be worth pulling all the data you can and seeing if there is a work angle you can leverage.
Brute force? Yes, but I don't like scammers.