I think I've got a solution to this...
Have them pay you (assuming they trust you 100% or you escrow the coins.
Than have them File a claim on paypal the next day.
You respond "They have been sent"
Have the buyer than close the claim saying "I have received what I paid for, sorry for the confusion, digital goods delivered 100%"
Dispute closed, it leaves escrow. And they have a hell of a time trying to refile it and prove anything to paypal..
Not sure if this is bullet proof? But I don't think they'd have much chance getting it back?
You can open disputes again with your CC provider, nothing is sure with PayPal.