I'm assuming you've read the details of Paypal Buyer Protection:
https://www.paypal.com/webapps/mpp/ua/u ... protection
Important: You may be required to return the item to the seller or other party specified by PayPal as part of the settlement of your claim. PayPal’s Purchase Protection program does not entitle you to reimbursement for the return shipping costs that you may incur.
Step 4: Comply with PayPal’s shipping requests in a timely manner, if you’re filing a Significantly Not as Described claim. PayPal may require you, at your expense, to ship the item back to the seller, to PayPal or to a third party (which will be specified by PayPal) and to provide proof of delivery.
The dude's gotta get the item back to you and provide proof of delivery (perhaps including a signature) at his own expense. His arrogant ass could decide he's not going to ship it back unless you pay for that, or maybe that he doesn't need to pack it properly, or that he doesn't need a signature.
Also:
The following claims will qualify as a Significantly Not as Described claim:
You received a completely different item. For example, you purchased a book and received a DVD or an empty box.
The condition of the item was misrepresented. For example, the item was described as “new” but the item was used.
The item was advertised as authentic but is not authentic (i.e. counterfeit).
The item is missing major parts or features and those facts were not disclosed in the description of the item when you bought it.
You purchased a set of three items but only received two.
The item was damaged during shipment.
The only thing that seems close would be if he was claiming it was damaged in shipping. If that's the case, it seems reasonable to initiate a FedEx damage investigation. Even if FedEx won't pay a damage claim, there's a least some burden on him to legitimize his claim of Significantly Not as Described. Would a FedEx investigation support his claim? Is there a chance he wouldn't cooperate with the investigation? Has he in any way substantiated his the basis of his claim?
If he doesn't do things exactly by the book, call it out to Paypal and reference their policy verbatim.
Also, I don't think it would be bad if his abusive messages got into the hands of Paypal. Where they have discretion, his dickishness could bite him in the ass.
Finally, have you searched the various forums for anything he's posted? I bought a preamp from a guy and one of the four channels didn't work. I ended up having to file a dispute because he claimed it worked fine, but I found a forum posting from months earlier where he was looking for assistance with the same problem I was experiencing. Maybe this cuntstain has a NAD posting out there somewhere. Maybe a pic on his FB page. Who knows. Put on your PI cap ;-)
Best of luck to you in any case.