Honestly, mining stresses a GPU a lot, but they really are designed to be run at 100% for awhile. I have had a few mining GPUs. The can be a pain if they come with a mining bios, but as long as you flash them back to a gaming bios they should be fine.
I bought an ex-mining RX480. It had code 43. I flashed it back and it worked fine for over a year until I sold it. The new owner says it works flawlessly still.
However, mining isnt so kind on PSUs since miners often use molex/sata to PCIe adapters, as well as other funky ways to power more GPUs than the PSU is designed for. This can cause many types of damage. I see tons of PSUs with burned-out modular ports and other damage because of this. Even if a mining PSU seems to be working when it arrives, there is no saying how long it will last since it has been abused.