I recently paid for a purchase off QTH with Pay Pal for a D-710A that arrived poorly packed and pretty well hammered (bent pots, etc...). Seller drug his feet every step of the way, pay pal would give him about a week to reply on three different steps, tracked my return package, then gave him another week to say he'd received it. He still never replied so Pay Pal relieved his "back up" credit card for the full purchase price and put it back in my account. It took a month, but I got my money back. The guy was a dirt bag... BAD HAM!
QRZ and WWDX at least have systems to track & ban problem sellers. QTH, not so much... Lots of "good" used radio purchases between the D-710A and a problem with an ICOM 706 that I received a few years back from a QRZ ad. 2M was out when I got it, but the seller jumped through hoops arranging shipping to ICOM, had it fixed and even aligned the HF, then had it back in my hands in one week. GOOD HAM
What ever you do, check your purchases right away. Putting in a claim on used electronics that you'd received a week prior could get dicey.
EDIT: Also, don't let the seller talk you in to a "gift" payment on Pay Pal to dodge the 3% fee they incur. You can't put in a claim for the box of rocks you received if you "paid" for it with a gift payment. If the 3% is a deal breaker with your seller, offer to split it with him if it's a good deal, or even pick up the 3% if it's a GREAT deal. Just make sure that your payment is for MERCHANDISE, not a gift, service, etc...