But they stress the hell out of the VRAM coz mining is limited by memory bandwidth. There are reports on 2nd hand video cards from miners getting rendering artifacts after only a few days of gaming.
DRAM is pretty durable but the controller, bus pins, and other parts would be the wear/tear in my opinion. Those other bits inside the DRAM could very well wear out.
Debatable.
A lot of these miners are keeping their GPU-stations inside of a garage with no air-conditioning (so 90F+ temperatures, maybe 100F+ ambient). These miners are going for the cheapest-of-cheap conditions, they weren't running a datacenter, but a mining operation.
I'm willing to bet that the vast majority of them never paid attention to airflow issues. Closets, garages, maybe even sheds.
While GPU cores are underclocked and undervolted (but not necessarily), the RAM is going to be processing at full tilt as quickly as possible, possibly overclocked and overvolted and therefore at even higher temperatures.
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Finally, buying used means having a very ambiguous warranty. You might not have anyone to send the GPUs to. Its generally not a good idea, especially now that new-prices of GPUs is below MSRP.
Honestly, we're not getting a temperature graph of these GPU's life. We're only getting assurances from some cryptobro that they treated their GPUs correctly (and no offense to the cryptobro community, but... there's a lot of lying scammers out there). Its not a trustworthy community at all.