Actually there was a story from a business owner who paid $1000 for first class back from Hawaii to California. He was sitting in his first class seat sipping orange juice when they gave him the bad news that the algorithm said there was a higher level first class customer who needed the seat and he would have to leave. He resisted they threatened to put him in handcuffs. He finally got them to refund $500 so he could sit in a middle seat in the back.
1. The guy legitimately booked a first-class ticket on the flight, and his reservation was secure.
2. The airline had some kind of maintenance problem with the aircraft, and as a result they ended up replacing it for that particular flight with a smaller aircraft.
3. The smaller aircraft had fewer seats in the first-class section (20 instead of 24, for example).
4. So the airline really had no choice but to remove some passengers from the first-class cabin by either booking them on a later flight or downgrading them to the coach section of that same flight.
5. Whatever "algorithm" the airline used was probably perfectly reasonable. Maybe they gave priority to frequent flyers, for example. Maybe that passenger was flying on that airline for the first and only time in his life, and the company didn't care about antagonizing him.
6. Maintenance issues with an airplane are covered extensively in the ticket contract, and the passenger really has no standing to complain about that sort of thing.