It doesn't happen often, but porkies are told, and we have to deal with the aftermath on-board. Not a seat issue, but just recently my cabin crew had to placate a very dissatisfied lady who was charged a fortune for excess baggage "because the flight is full" ........ we had one hundred and two spare seats.
What absolute crooks we looked. I was ashamed.
Sure, excess baggage charges are there to discourage us becoming a removal truck - and bring in revenue, but she wasn't complaining about the excess charge at all - but about being told a blatant lie.