This happens all the time. And the other airlines also do it.
That doesn't make it right. If I pay for a seat that I chose, I expect to get it when I board. It's only right. It's like getting in a grocery line, paying for brand name crackers and, just before I get out the door, an associate tells me I have to take the generic brand because another customer wants the brand name, then proceeds to pay me the difference.
WTF?
