"Yes, we learned that from now on, we should ask passengers to turn off cellphones even earlier before takeoff ..."
There's such an easy solution here: Just ask who's easiest to bribe. Seat auctions, as they are known, used to happen all the time back in the '70s, those mystical days of your parents' youth, when candy was a penny and politicians at least pretended they were trying. The process is simple: Whoever accepts the smallest amount for their ticket gets paid (off). If no one raises their hands at first, you up the reward until some slacker figures he'd rather buy a 4K TV than get home on time. And it worked really well, until airlines realized that saving two microseconds of income and bullying people out of seats would be a lot more fun.
United, if they weren't so busy letting sexual assaulters walk out of their airports, could learn a thing or two from Delta, which has taken a novel and slightly devious approach to the seat auction. When you check in on a Delta flight that's in danger of being overbooked, they will ask you in advance how much money you'd accept in exchange for a later flight, so they know beforehand whom to approach if they need to bump someone. It's basically a blind seat auction, and it helps Delta get planes out faster while kicking fewer customers to the curb. It might dash your hopes of getting $5,000 for your seat and throwing a legendary party, but ... actually yeah, that just sucks.