While at a show this past weekend I Saw a nickel model 18-1. I know Nickel? It looked right, a 4 screw ,1959 or 60 gun. I removed the grips and the only markings was a small N with a line of numbers next to it. It didn`t look like a date. Anyway I tried to buy it for 650. The seller said he didnt know what he wanted for it so I said I would check back. 12 minutes later he said he had sold it for 600. Within 20 minutes the new owner sold it for 700. I`m just wondering what a true market value would be assuming it was original. Any thoughts? I know where its at & may want to make an offer.