But how do you know that the card wasn't run to the point of damage when you get it from EBay.  Sure, it may work for games, but 98-100% GPU usage day and day out will reveal the damage.  If you get an EBay buyer who has a history of buying a higher end card on Ebay and selling their lower end card [and they indicate they are gamers], then it might be a safer buy.  I have no problem buying or selling cards on Ebay, but for this particular purpose, I am wary.  You may or may not get what you pay for.  Whenever ATI/AMD puts out a driver, a problem is likely to crop up which may or may not cause you difficulty ... will you blame it on the card [and seller] or the driver?  You won't ever know for sure.  New with warranty is my suggestion for mining.  No doubt others feel differently about this and that others have had success using Ebay, but YMMV.