PayPal TOS says they will NOT accept signature / tracking number alone for purchases over $250 USD.
For amounts over $250, additional documentation, such as a written contract may be required ... and in any event, PayPal has a year cap of something like $5,000 (I don't recall the exact amount); intangible goods, like domain names, are not entitled to any protection ... as in $0!
And finally, many seller protection provisions are limited to transactions that occur in certain select countries - if either one or more of the parties is outside those areas, then PayPal seller protection may not apply at all.
Your best bet is recovering the domain, if you still can - it really depends on the registrar, and your contacts with them; may take some communications on a backchannel so to speak to get it back.
With that said, if the amount in question is relatively small to you, then it may better to chalk it up as experience (ie. screening buyers better in the future) and move on.
Good luck.
Ron