I would have to have more specifics about the item, but Paypal is particularly interested in three things in this instance.
1. Is the item not as described in a significant way?
2. Is there a tracking number?
3. Did the buyer make a reasonable attempt to return the item.
Now, on 1, did the buyer lie? Did he say he bought a brand new Lexus from you and you delivered him a scale model? Or did he say the color isn't what he wanted?
With 2 on your side, you are 90% of the way to Paypal's heart. If you can verify you shipped SOMETHING, especially if by the time they resolve the dispute, it was delivered, then Paypal will most often rule in the seller's favor unless the buyer can demonstrate their complaint clearly. That takes a bunch, photos, etc. etc.
If you negotiated in good faith to take the item back less shipping expenses and explain that the item was not significantly different from what was in the listing and explain this, I think they rule for you.
Why? I had the same problem. Woman bought a jacket from me. Got it in 2 days, thanked me, said she loved it. Three day's later, buyer's remorse, wants her money back (makes up a stupid excuse). Item is no longer new, she files the same ("item significantly not as described") against me. This was a $200 jacket. I worked with her to get it back etc. and she was a real snot wanting all her money back and me to pay the shipping. So I let Paypal rule. They said the jacket was as described even though they never saw it.
If the buyer has the item, and has made no effort to return it, then there is no beef. What you have to really worry about is if you can't produce a tracking number. That always goes in the buyer's favor.
The cancel the credit card idea is not a bad one, to prevent paypal from nailing that account. But make sure you also don't have enough in the account to refund when they make their ruling. If there are insufficient funds, paypal may rule in the buyer's favor but they just tell them, sorry, no money. I always keep my account drained.
Paypal will do a reasonable job assessing the problem. If you have evidence submit it. If you have more evidence than they will let you enter, send it to
resolution@paypal.com referencing the dispute number.
Remember, the fact you are 6'7", or even 6'6 1/2" does not make you right. It only makes you 6'7". Assault charges are far worse than even losing 5K. And the lawyer and police won't care about something that insignificant as they bill you and put you in a cage. Bunk not long enough? Too bad. Finally, if the guy has a gun, all you are is a bigger target.
It is stressful. Some buyers are horribly unfair and major pricks. But don't make it worse. You can still sue if need be.