Yes this is terrible. On the other hand, if your goal is to prevent people from signing up using disposable domains, the blacklist approach (which I have tried

Yes this is terrible. On the other hand, if your goal is to prevent people from signing up using disposable domains, the blacklist approach (which I have tried before) is a never ending game of whack a mole. Sounds like this was in person at store though which is extra weird because seems unlikely that scammers would be trying to sign up en masse at a physical location (unlike if the form is connected to the internet)