There are few types of these cases: 1. They say that they don't have enough money and have no one to come and pay for them. 2. They try to sneak out when you don't pay close attention to them. 3. They walk out of the door complaining about how horrible the food is and have no intention to pay. They even say that you could call the police. (of course we know that when the police come, they will be nowhere to found).
I mean, I work in the restaurant industries for a long time. I've seen so many of these cases. I've always think that maybe because of our race. The customers always do that to us. Does that happen to other cuisines too?