Many if not most of the guns you're looking at are being sold on consignment. The willingness to negotiate is likely affected by the actual owner's sentiments as given to the dealer. How long the gun has been on the market is likely a factor among other things. Never hurts to give the owner a chance to say "no" as he has a desire to have cash instead of that gun.
I bought a nice English gun a year ago that I knew had been on the market for over a year. I made an offer at about 89% of the asking the price and bought it at 90%.
