How cheap are these cards? If they are used for mining for long already? I don't like used GPUs mist especially AMD cards cos they die easily, I bought 3 Radeon GPU as used from someone and later I detected that they've worked and solder some things on the GPU before, this was after the GPUs stopped working, the choice is yours
And i like used AMD cards. I have 150 AMD cards, many of them are used and they run for 4 - 5 years now -> 1 died in this time.