I understand the financials involved in overbooking, but I still think it is an unacceptable practice - I've never been "bumped" off a flight but if I was I would be furious having gone to the effort to pick a particular flight and make plans.
Flybe don't overbook, 78 seats on the aircraft, 78 offered for sale and that's how it should be in my mind.
When you order a new car, you don't turn up to the garage to be told "we don't have, and never did have, the one you
actually ordered and paid for, but you can just have this one instead"