I do not envy you. I do agree that we (the consumer) frequently act inappropriately and then expect to be treated fairly. You sound so frustrated; perhaps you could coin a few phrases to help you in trying moments. If a customer wants to gripe about another customer, you might try, “I don’t mind, after all they help pay my salary just like you do.” As for the money thing, making eye contact prior to the exchange of money may help; of course, nothing will help some people, including me on a bad day. On behalf of customers everywhere – I am sorry.