Keep in mind though that when an airline offers money for you to voluntarily give up your seat, they're usually talking airline dollars. In other words, if Delta offers you $800 dollars to give up your seat, they're talking 800 Delta Dollars---to be used on Delta in the future. Cold hard cash usually only comes into play when you're forced to give up your seat.
I had this problem with Delta and I have never used them since.
London to New York flight my tv did not work and for the 7 hrs 55 min journey they offered me a free newspaper.
I asked to be moved and the plane was apparently full.
So when I complained I got a £50 voucher for my next flight with them. I pointed out that I would never ever use them again as a free newspaper to read for 7 hrs 55 was a complete joke.