It was certainly a major problem, if you bought a new car but the dealer gave you one with 50k miles on it would you shrug it off if the gas mileage was still the same? At a basic level it's fraud.

There are practical concerns as well, these machines are usually pretty poor quality and the immense heat + poor cooling typically means the chips will burn out one-by-one over time. The PSUs are especially poor and will burn out and need replacing as well. Getting a used ASIC means these will be problems sooner.