Secondly, why do airlines even have carry-on limits if they don't enforce them anymore. I was dodging huge bags that people were trying to pass off as carry-ons that were twice the size of the little 'this is the maximum size' displays at the gates.
It might just be a US thing. Flying through the EU and Russia, they inforce the hell out of those limits because they make a nice bit of profit on them. I took the wrong case once on a flight between Berlin and the UK. I thought it was the right size for carry on, but it turned out to be about 5cm too large, so I had to put it in the hold. I can't quite rememeber the cost, but I think it came to about $60/£40.
As for selling your flight to someone else, have they offered any compensation? They damn well should do.