Back in the day, I wasn't born yet, when my dad was a mechanic at a Shell gas station, he had to work the register one day.
This guy came in and he bought a dollar worth of gas. [This was back in the late 70s.] He paid with a $20 and my dad gave him change. The guy started to leave and turned around and said he didn't give him the right amount of change back. So, my dad had to give him the change back out of his pocket because they lied.
Next week the same guy came back and did the same thing. Unlike last time, he counted it back out to him. He started to turn around and tell him the same thing and my dad said, "Hell no! You liar! Get the **** out of here and I never want to see you around here again!"