Cards used for mining is far more worn than a gamers card since they probably been running at full speed 24/7, causing solder, glue, components(capacitors in particular) and print board having far more heat damage and fans being pretty much worn out. To buy a card from a miner would be a very risky thing, and only be considered at a massively reduced price(1 fourth or less than retail).
A smart miner would buy the cheapest cards possible, using a overclocked premium card for mining makes no sense, it would be downright stupid to do so, a smart miner would under clock the card to make it more efficient, so manufactures that don't want them to be used for mining should focus on premium cards.