There is an app called Seateroo http://seateroo.com/ that allows passengers on a plane to swap seats with each other for a fee. And Seateroo takes 15% of the fee the 'buyer' pays to the 'seller' of the desired seat. But if the transaction doesn't happen, they will refund the entire amount to the 'buyer.'
I like innovation and think this is a good idea but it needs the blessing of the airlines or the airlines could do this themselves. Without enforcement this will never work.
A couple of scenarios:
1) If a buyer and seller agree to a price and they swap seats, then the buyer claims the transaction didn't take place once they land and have reception again, the buyer gets the money back and got to sit in the better seat for free.
2) Or if the seller won't move after receiving payment, who is the buyer going to complain to? The airline won't care and this may even be against the airline's rules to receive payment for swapping seats.
Also, you need internet connection to make this work, which means you need to do the swapping before the flight takes off, what's to stop the seller from initially swapping seats, then once in the air, goes to the flight attendant and says 'hey this person is in my seat' shows her/his boarding pass and gets the buyer kicked out. Again, the airline isn't going to care about an app.
I suppose you could have an eBay type of rating system for rating buyers and sellers.
Perhaps the app builder is just looking to get acquired by an airline or someone else. (like 500% of startups are)