I failed to mention, under no circumstances regardless how late it is, what the complaint is, should a customer be treated with anything less than courteous behavior from any manager or person in charge, at anytime.
In the words of a boss I had many years ago, "You are dealing with the public, and I don't care if your dog just died, keep a smile on your face at all times. And if you can't do that, you can't work here."