The first Suburban I bought I took the 3rd seat out immediately, I got extremely tired of it being in the way in storage and finally asked the auto salvage place if they bought them, they said no, they had more than they needed, i asked if i could give it to them, they were OK with that. The next Suburban I got, one of the first stops was the salvage yard to get the da*ned 3rd seat out of my life as soon as possible. I was happy to drive away from it with less annoyance in my life and concern if I was losing money by giving it away.
YMMV, to me just getting something like that out of my hair was worth any perceived loss of money I may have gotten fussing with them trying to sell them. I consider it one of my best investments in vehicles, the gas to go to the salvage yard to get rid of the seats.
If nothing else, Id advertise them as free, but limited time offer.