I bought a Gigabyte Windforce r9 290X used off eBay most recently.
I asked the seller for the original receipt which he provided no problem. He said that i'll see that I got a heck of a deal... which I did
I intentionally wanted to get one that had an extended burn-in period. Not my first R9 290x Windforce, as I bought a NEW one which died sometime after 5-8 hours of use and had to be returned. return shipping (with insurance) was over $20
Before that I bought my 2nd MSI GTX 760 Twin Frozr used and saved only about $30 on that one, but I also able to get the original receipt for that one. I registered it online with MSI and uploaded that invoice and the UPC.
For the R9 I really did not need an invoice, as I still had the one from the defective board. Still, I think its good to ask for it just to see if the seller is able to provide a intelligible response prior to placing a bid. I also read through their feedback history and see what type of things they typically sell. Also you might also ask the seller what the ASIC quality is from GPU-Z
there is no way Newegg or Tiger Direct are going to give you that info
good luck! cheers!