I once played in a one-shot at Origins Game Fair that was supposed to be a Savage Worlds game. However, the gamemaster wasn't even close to following the rules correctly.
It wasn't just things like misremembering how grapple works. Oh no. Instead, PCs were being damaged by Fighting rolls (thus making Parry useless), NPCs were mysteriously rolling "dodge checks" to get out of an attack from the players (but the players weren't asked to do the same), and the GM was spending bennies to make players reroll their dice. Players familiar with Savage Worlds will know that these aren't even close to the real rules.
To be honest, I got the impression that the GM saw the rules for the first time 15 minutes before the session, and then just made us stuff on the fly. I offered to help with some of the rules, but he just said "I'm more interested in fun than playing with the rules".
Unfortunately, the complete and utter lack of following the rules made me have a miserable time, as I felt like I was just playing to the whims of the GM.
Is there anything I could have done at the time to make the situation better? If leaving was the best option, how should I have done it? Could I have done anything after the session, like talk to convention staff?
This question is similar to What should a player do if the DM doesn't know the rules?, but seems to be written with a home game in mind instead of a convention one-shot, and the situation I've experienced appears to be even more severe.