It sometimes happens through no fault of our own. We ask for the bill, telling the waiter we will pay by credit card. On the card machine it comes up as refused. Second attempt and the same thing happens. The waiter suggests we pay cash, but we do not have enough. Either the card is suspended because someone has fraudulently used it, or our credit limit is maxed out. If we are a regular customer, we will be permitted to leave on the promise of making a bank transfer or returning another day to settle the bill.
Sometimes restaurants claim their card machine is not working so that they can justify requesting cash. This allows them to keep the transaction off the books and untaxable. The average customer does not really care but the inconvenience caused is selfish and unlawful. More disturbing is adopting similar tactics to defraud the restaurant owner when he or she is not present. The employees agree between themselves which customers to con and how to split up the illegal loot.
Occasionally people have no intention of paying. I remember seeing a man at an adjoining restaurant table enjoy a superb lunch with a bottle of expensive wine. After his coffee he informed the waiter that he could not pay. I never saw the final outcome, but one thing is sure: he would not have been asked to wash the dishes, as the old myth used to have us believe. Nor is calling the police a cost-effective alternative. Writing off the loss is the commonest finale.