I once had a dbag come up to me and try to pressure me to swap to an inferior seat. It wasn't a terribly long flight but it was a couple hours in an inferior seat and I had picked my seat on purpose, so I said I'd do it for $100. I thought it was a reasonable offer. He proceeded to cuss me out then and again later leaving the flight.

I haven't bothered with it again, even though it a simple cash transaction is the easiest and fairest way to accomplish these sorts of switches. Now I just say no and fiddle with my headphones as an indication that I am listening to something other than the dbag.