The biggest problem that mining GPUs tend to all suffer from is fan failure. I'm speaking from experience.
Replacing a video card's fan is certainly doable, but it isn't nearly as easy as replacing a CPU or case fan (due to the fact that so many GPUs have custom fan setups).
Some of the GPUs (like Sapphire's) have fans which are easier to replace. These are not the norm. Also, being easy to replace doesn't mean they are easy to acquire.
I'd take a mining rig GPU for a discount.