My favorite negotiation was at Nicholas Smith booth in the orange hall a couple yrs ago. There was a Lionel SP black widow b-unit for I think $140 written on a yellow post it note. There was only one piece there. It was boxed so I was reading the label and looking it up on the net trying to decide if it would look ok and did I really need it. I think it had railsounds,etc. I had a postwar F3 that someone beautifully painted SP black widow but kind of a matte finish.
A Nicholas Smith employee walked over and took a magic marker and crossed out the price and put $120.00. He looked at me and said "that's why these pens are called magic markers. They have magic in them". I said "well I don't have the other matching pieces, but if it gets down to $100.00, I would have to buy it".
He took the marker and made the price $100.00. I said that is a magic marker. We both laughed. I picked it up and walked over to pay.