that is fine to buy used equipment,  cars, vga cards, cpus and etc. people used to do it for a long time.
a lot people bought used ASICs after proper diagnostics and they worked as intended.
sure there is more risk against new equipment but the price 2-4 times less and that is totally fine reward for the risk, imho.
based on fact that profit is reducing very fast, purchasing  used equipment may allow to ROI faster.