Why all the concern about the low ball offer? Certainly the shop isn't going to pay anyway near what they get a new gun for wholesale. As has been stated, most shops will offer 60% of the going used price for a gun that they know will sell. They may not really want the pistol very much for a number of reasons. These shops have overhead and must work at a profit. Gun folks seem to get all upset that a gun shop wants to make 20%-40% profit for selling a gun, but will go to WalMart and pay over 100% profit for some clothing made by a sweat shop in China.
As has been stated, attempting to make a private transaction in a gun shop will get you thrown out. I don't get my feelings hurt by someone offering me a low price for a gun I have for sale. I simply say, "No thank you!" I have gotten a little ticked by someone on here asking what my bottom price is and then offering me 20% or more less. I was at a gun show and a guy (sitting along the wall) said he was interested in a gun I was carrying around. After telling him how much I was asking, he said, "I have a table and I have to resell it for a profit, so I could only pay this $_______." I thought, "Really, that sounds like a personal problem. I want to sell it to an individual who wants the gun to shoot!" Still, I didn't get upset at the guy for the low ball offer.