Many years ago I purchased a new, not new model, Ruger Blackhawk 3 screw flat top in 41 magnum from a pawn shop for just what they had in it, slightly over $100 bucks. The fellow never came back to get it and I wanted it bad. He was asking quite a bit more, but after several trips by to drool over his counter top he let me have it for his cost. Both of us were happy.
Several years down the road, even knowing what I had, I swapped it even for a used Redhawk in the same caliber. Again both of us were happy. I knew then that the BH was fetching more in the condition I kept it and the model it was. Even so I had originally wanted the RH and even finding one used back then was unheard of.
On another occasion I walked into a local gunshow and carried in my pop's old Colt Army Special in 38 SPL. Several vendors were VERY interested in it, and offered me up to $400 in cash then and there. I didn't really have a clue as to the worth other than sentimental to me, but figure if they were willing to offer me that up front, I might well just hang on to it for a while.
It works both ways no doubt. Just as long as nobody is left feeling screwed over it usually works out well. Carma however, has a way of working things out in the long run though.