My experience from a couple of years ago when I took 2 of my boys to Eugene for the 62-20 game.
They overbooked the flight back to SLC and asked for people to be bumped, and then randomly bumped us.
We had to take the next flight out which was the next morning.
I found out the airlines have a deal with the FAA on overbooking.
If your next flight lands one, two, or four hours after your original flight lands, they have to give you 2x, 3x, or 4x the cost of your original 1 way ticket price as a fine as well as a free flight.
This is why they offer you $200-$500 in vouchers. It ends up being cheaper than the fine.
Since the next flight for us didn't go out until the next morning, and the 1 way ticket price was roughly $300, we got 3 checks for $1200 (the 4x fine). It worked out well for us since we were staying with my aunt and uncle in Corvallis, so we just went and spent the day with them and flew out the next morning.
The whole trip originally cost me about $2000 for flights for the 3 of us, so Delta basically paid me me a couple thousand dollars to pay for me and my boys to fly up and watch Utah kick Oregon's ass and spend the weekend with family.
EDIT: That's also why they start with the cheap seats since the fine is based on your ticket price. These are the things you find out when you don't freak out at the counter people since they don't have any control over this.
EDIT2: The reason they have this deal is because a certain percentage of people don't show up for their flights, allowing them to maximize their seat usage. We don't hear about how many people don't get bumped because someone didn't show up. It must work even with the 4x fine schedule since they do overbook on a regular basis. It blows my mind that people don't show up for their flights.
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