There is lots of urban lore about coach passengers on airlines being magically upgraded to first-class seats, but less is said when it happens the other way around. But this does happen — a lot.
Typically, airlines do not charge more for passengers being bumped up. But those who paid extra for a special seat have a case for getting something in return when it is taken away. Yet when it comes to such involuntary downgrades, consumers are often left on their own to make the case that they should get something back.