Pastorbass,
There's a couple of different takes on this. As a seller, the fairest price, is the most you can get for it, and fittingly, as the buyer, the fairest is the least you can get for it.
If the guy is a friend, the fairest price is one that you are both happy with. In fact, that is the definition of any good deal. It's a price where both parties are happy with the price. It doesn't matter if you can get more for the TM, if you are happy with the price and your friend is happy, what more is there? Say you can get more for the trolling motor, but by trying to get the higher price, and you lose a friend... what then? Remember that spinnerbait holder I sold you? I could have gotten a much higher price if I wanted, but I didn't. Do the right thing, and you will both be happy.
Good luck.
Tight lines and God Bless
Danny