Yes that is the flaw, but it's where you cross the line from being a generous ebayer to a defensive by the letter type of ebayer. I just bought something from someone who went out of their way to burn drivers and such like onto CDs for me, when they didn't have to at all. Now I will definately buy something from them again without hesitation and will recommend him to others.
Honestly, it is fairly hard to blow a gfx card unless you are really clumsy - and there is no way you can really prove that it wasn't damaged in the post. If you get the card back have a good look at it's physical condition - postal damage can be visual. If it's physically ok, but there are electrical problems in your rig then maybe he did something to it, I don't know if there's a way to tell. Either way I would as a courtesy to customers always give them the benefit of the doubt. Chances are it will work fine in your computer.
However, you seem to be a by the letter type ebayer and you did clearly state on the ebay page 'no refunds' and sold 'as is'. That would be enough to put me off
(but you still sold it for a good price, fluke)