but nobody needs to know what load they were used so it's "barely used" on the listings

load isn't what causes degradation, it's heat and as someone who has mined crypto for years I'm aware that there are a lot of things that can be done to run hardware quite hard and keep thermals low. Whether or not that is what is being done, I have no idea. A GPU mining crypto for 5 years kept below 65C (rather easily done) is going to have far more life left than a GPU in some kids gaming PC that spikes frequently to 85C for even a year.