Forget about submitting the dispute using paypal web site. Search Google for paypal support/scam emails. Paypal has a lot of emails where you can send logs/scansto open a dispute. Send them to two or three different addresses. Explain he is doing this to other people. Paypal hate people that use them to sell bitcoins (actually, they hate bitcoin and is against their TOS to sell currency), therefore they might go along just to teach a lesson to the seller. Of course, they might decide to teach both of you a lesson, freezing his account, but without paying you back. Typical paypal reaction. But at least he will get a lesson too.
Google also his email/name accounts; usually, you will find other emails/accounts he is using on other websites and you might find other paypal accounts (or other reversible systems, where you can try your luck) that he is using, just in case that one is empty of money.
It's very easy to track a seller on the Internet, they all use foruns, etc.
You might end up finding his facebook or other private info and then you will have means to go to authorities, threat him to write to his family about him, etc. Basically, make his life miserable.