Turns out the seller got cold feet at my offer. He thought my offer was fair, but it is far less than he wanted. He said he may just pack his TurboDuo games away again.
I think he is under the impression that the games he had to trade are only going to continue to go up in value. I have to disagree with this theory, especially after the flurry of sports cards collecting in the early 90's and toy collecting in the late 90's proved that values will indeed go down. Probably not for everything, but the idea of infinite growth is kind of weird to me. It just doesn't make sense how people can think that, since history tends to prove that line of thought to be folly. Sure, my games may retain some value, but I really don't rely on the idea that what they are worth now will stay that way. Nor do I think they will continue to climb in value.
He didn't have a Duo either, so he can't play the games he had to trade either. Seems like a waste. Oh well, I guess I have to have something to aim for with game buying. Maybe one day....