"Would you buy a second hand graphics card that had been run at 110% 24x7 for years, the MTBF has been eaten away."
Yeah, if the price is right. I've had a $20 SSD wear out (in less than 6 months; I was running extremely heavy write load on it though) and a few cheap SD Cards. But, GPUs, CPUs? If they're run under the temperature limit, I've never had one fail. (Most likely, for me, the price would be too high for me, they'll want too much for them. But I'm just saying, MTBF would not be the reason for me not getting one.)