Depends on what is was mining and how it was configured. Most of cryptocurrencies that have been popular to mine with GPUs recently don't load the GPU 100%. And the cards are typically underclocked and undervolted to reduce power draw, which would reduce load on the card. As long as you get a suitable discount on account of the card being used, I wouldn't worry about it.
@Ramlethal having a sustained, consistent (moderate) load can actually be better for electronics, as you then avoid thermal cycling which can result in mechanical stress on components. Also, you can't flash custom BIOSs on Nvidia cards.