A few years ago I was flying from Atlanta to Honolulu when a fellow passenger made an offer I could refuse, and did.
The gentleman wanted me and the passenger sitting next to me to move. It seems that the petitioning fellow and his wife were sitting separately. After determining from my seat mate that the said seat mate and I were strangers to each other, the gentleman proposed that we give up our seats so that he and his wife could take them and sit together. After, all what would it matter to us?
My seat mate agreed to the deal but I declined, much to the ire of the wannabe seat trader, who complained loudly for much of the remaining flight time about my intransigence. It was a nine-hour flight but it seemed shorter. The guy was so entertaining in his outrage the time just flew by.