I have sold a few GPU's on eBay over the years along with other hardware. I don't do auctions, I go straight to the 'Immediate Payment Required'. I also have photos of the card, the packaging and serial numbers. I put in the description about the serial numbers listed and the card photos etc, also put in as many photos on the listing as I can showing the card. I also send the cards by Royal Mail Special Delivery with insurance to the value of the card, if you were buying it new, it costs, but Its never let me down. (always add P&P to the listing price) I also put in the description that it will be sent by Special Delivery and that means there is a comprehensive trail of the card being posted to the point it is handed to the person buying it. All that tends to put the time wasters etc off.
I did an auction a while back (which was a mistake). The person buying it, had a UK address and it looked ok (I have a lot of postal exceptions) I looked on Google and found the house. I did a search on the buyer and found out he was a visiting student from wait for it......Nigeria...... I sent a couple of e-mails to him, which he didn't reply to, nor did he pay for the item. I bet he thought I would just send him the item??? Yeah, like that's going to happen. After a week I put in a claim for non payment and got my fees back and blocked him from buying from me again! This is why on expensive stuff I always go for the 'Immediate Payment Required'.