Is the transaction finished and unable to file a dispute after positive feedback is left?
Tell him before he leaves to leave you positive feedback saying he got the item and it was in condition as described. Also maybe check his license to make sure it matches the paypal name, otherwise probably just using a stolen card.
The answer to your question is that leaving positive feedback has no bearing upon whether the buyer can file a dispute with Paypal. Seems odd, but true.
I sold a used industrial ultrasonic cleaner that was quite pricey and sold for around $350. It was sold as used and as as-is. Buyer receives it, tests it, and leaves positive feedback.
About a month later or so (remember, you can file a Paypal dispute up to 90 days after the auction ends) he files a dispute. I file with Paypal that the item was shipped, he received it (sent UPS and all tracking info was there....), yet the buyer got the dispute completed in his favor, despite leaving positive feedback for me.
Maybe the cleaner died after a month after use, I don't know. He never responded to my emails. All I know is I was left with a Paypal account with a negative balance and I won't use Paypal ever again.
Good luck!