It is inevitable that when you work a customer service job, where you touch the moneys and talk to people, you will have a deal with a grifter once in a while. I have no patience for these people.
The novice clerk is quickly confused and a grifter's dream. Their grifter tricks (switching bills, making claims, tandems, demands) throw a new clerk into The Customer Is Always Right mode and they give them the $20 bill because, surely, they, the clerk, made the error and they don't want to anger the precious customer.
The seasoned clerk knows these tricks and is not intimidated. How dare they endanger my job by trying to trick me out of 20 bucks! Or whatever amount. Fcuk off grifter. You say you gave me a fifty?? I say you gave me a 10. (This grifter trick is especially juicy if there are none of the bills they claim in the till). You don't believe me? Well, I will call the accountant down to count the till and she will compare it with the days sales. And I doubt you have the guts to stay for that truth session.
I don't believe that anyone should be taken advantage of or robbed or milked, but the people that rip off stores via the clerks til are especially low. You don't want to piss them off. I remember faces and I will tell everyone what you do.