I think I would have a bigger problem accepting money for my seat, then saying 'NO THANK YOU', when other passengers are watching for your reply.
On another string, I reported on a recent flight, that I had an aisle Emergency row seat for which I had driven to the airport (40 miles R/T) a few days earlier to get assigned. A women in the middle seat with husband in middle seat row behind asked me if I would....... I immediately replied 'Don't even ask'! She said the desk agent told her to ask for someone to change. Obviously, they didn't plan ahead AND checked in LATE. This has got to be my shortest fuse. Anyway, Her husband traded wiith her and was a little pushy the whole flight! I couldn't help it, if he was 6 foot plus! He should have planned ahead, if they were not standbys!
In this case, I wouldn't have changed seats for money!