Exactly! There is no reason that front-line clerks should be forced to act as mask police. Particularly in the US where you've got idiots with guns wanting a fight about their 'rights'.
If anything, in these times, the manager or supervisor should be up front, sorting the sheep from the goats.
I am the Assistant Manager, and if I'm at work, I'm the manager on duty. I barely have time to serve my customers and try to keep the number of customers in the store down to the law mandated 5 at a time (there's usually a lot more in the store waiting). I certainly don't have time, nor inclination to battle the customers over masks, not for 16.50 an hour. We are understaffed, and over-worked as it is.