Especially at restaurants.  It's a common tactic.  They'll say there was a mistake in their almost-completely-eaten order--but they don't want you to take the bad food back to the kitchen, they want to keep it too and get the replacement.    One place I worked at a had a table who rang up a large bill then texted the manager with a sob story about "our waiter threw tortillas at us" ("threw tortillas at us" because it was a very large table and he had to reach across it to give everyone their tortillas).