For example:
Customer walks in without a mask. An employee can either reach in the drawer under their register to get a mask and hand to customer,  or the employee can walk over to wherever the customer went in the store and ask if they need a mask while holding it out for them to take.
#1. Customer gladly takes mask while explaining that they forgot their’s somewhere.  So the employee did a good thing.
#2. The customer sees employee walking while holding mask and will instantly get mad. When employee asks if they need a mask, world war 3 is about to start. So employee did a bad thing.
Even if the employee did nothing different…their good/bad thing depends on how a customer reacts to it. It has nothing to do with following the rule on the door. The customers reaction dictates what is considered “professional”. 

I forget how many different airlines now have turned planes around and interrupted flights because 1 or 2 passengers refuse to wear masks. Was the pilot unprofessional when they disrupted all the other passenger’s flights?   Could all those other passengers be compared to customers in a store? Do you allow one person to get away with breaking a rule, just so you don’t cause a scene in front of anyone else? Even if that rule might effect everyone else. 

If a store doesn’t  have a sign on the door stating “No shoes, No shirt, No service” and very rarely do we have people come in without those items. But it does happen. Do people get offended by businesses that do have those signs posted? So if they don’t mind being  forced to wear shoes, then what’s the difference in being forced to wear a mask?  
I mean when was the last time we heard of anyone complaining about their freedom being taken away because they HAD to wear shoes, or a seatbelt?

What exactly does “professionalism” mean? How should retail employees deal with anti-maskers in 2020? Yes, please this is a very real issue in my store so if you have ANY opinion or advice, please leave a comment.