......only if they're wiling to do so.

Earlier this month I had a FA who wasn't even willing to help boot a seat poacher from my seat, so I had to play the bad guy and tell the person that I wanted to sit in the seat that I had reserved when I purchased my ticket. The poacher had apparently been upgraded at the gate and she somehow decided that she liked my seat better and just settled in without asking. Given the seat numbers, it could not have been just a mistake unless she was illiterate.