yes, there are extenuating circumstances.... but none of my employees will ever say that they refuse to serve a customer.
Now if the customer is sitting there naked... if the customer has a bomb strapped to them... if the customer smells like a homeless garbage diver.... yes, these are instances.
But as far as tipping.... you have a whole day with good tips from good customers and part of the business is putting up with that small fraction of bad customers WITH A SMILE.
I am not in retail service but I do deal with customers all day. I take the good with the bad.
You are right a manager should support his staff. But I imagine his staff has a few customers who tip more than required and they surely are not fussing about that.
If I'm the manager, I knew about this customer long before an employee refused to serve that customer. I would rather an employee refuse to serve a customer than to spit in a customer's food.
That's why I left customer service and sales; I knew I was reaching the point where I couldn't interact pleasantly with people anymore.
Enjoy your day (for real!)