Because of a glitch on Flybe's website, I booked Mrs Scunner on a flight to Belfast that came out as me when it came to printing off the boarding pass, as it was booked with my credit card. I phoned them 2 hours before we left for the airport (when I had just tried to print off the incorrect boarding pass) and they were fairly accommodating although not apologetic. They said for her to check in at the airport rather than go to the gate.
This she did, and was charged £30 because her hand luggage was too big in one dimension. When she got to the gate, she was surrounded with people who hadn't checked in in person, most of whom had hand luggage far bigger than hers - but they weren't checking it at the gate, just at the check in desk.
So their mistake cost us £30.