I remember when I was 14 years old getting bumped from WT to CW on a flight from LHR to LAX. I'd just got comfortably settled, and was feeling quite pleased with myself at having landed a super nice seat, when a FA made the announcement (pre-take off) that a passenger in the WT section was offering 1,000 USD in cash to switch seats with someone in Club.
Obviously a bum deal if you've paid for your own ticket, but if your company pays, a nice little earner I guess. Anyway, the businessman I'd been plonked next to was, I doubt, too enamoured to know he had me for company for 11 hours, and suggested I jump at the chance! However, having aquired a taste for the finer things in life, I didn't - and a few minutes later some other bloke in a suit swapped seats.
Never heard / seen something similar happen on board these days... in fact, I was suprised they even allowed it back then! But there was a part of me which regretted it later on that holiday. I mean, that was a lot of money to a 14 year old! I doubt BA would have been too impressed at me profiteering from their kind gesture of an upgrade, anyhow...