I consider myself lucky that I have never had a serious seating problem, but then I usually travel by myself. One time though, UA turned a seating problem into a seating jackpot situation:

HKG-ORD 14 hour flight. Lost my preassigned exit row seat for no reason. Complained in a very polite manner to the check-in agent and got her sympathy. She called the gate and was told all exit row seats were long gone. I jokingly suggested a business class seat, she said there is no guarantee and asked me to check at the gate. Well you guessed right, I got an op-up! The ticket was also an award one. I was very happy.

Now I don't really expect anything like this happening again to me very often. OP's story just made my blood boil. Some UA FAs are not known for their willingness to help.