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
Not all used GPUs are bad that's why it's most important to buy from a trusted source, I use an agent in China that helps me test the GPU very well before sending down to my country for me, I have many used Nvidia GPUs too but I got them because new GPUs are high in price new GPUs are always better