If you have a seller like me, and it doesn't work when you get it I will refund you your money and pay for shipping back to me. Then again I don't sell GPU that don't work. I have a second 1070 sc2 going up for sale end of this week
I've purchased used cards on ebay and craigslist for years. Great way to get some value. Just make sure you have a way to check them before paying for them.