You have to get lucky, and time it right. Don't be afraid to make an offer, the worst they will say is no.
I got my second, and almost new looking Dan Wesson Model 15, 4"VH at a pawnshop. I hadn't been in for a while, and when I saw it, I didn't ask about it much, there was a 1911 that I pretended to be interested in, instead. I looked at the 1911, and kind of shrugged my shoulders, and then I asked the guy behind the counter, "What's that?". He made a face like it smelled and said, "That's a Dan Wesson .357!". I said, "Dan Wesson?" He nodded and I asked to see it. I pretended not to know about the interchangable barrels, and asked how much he wanted for it. He said, "Well, it's been here a while, and I was looking for $125 for it, it has the box and the tool and stuff with it, too".
I looked at it for a while, and at an old rough looking Beretta 1934 that he said shot ok, it just looked bad. He had a bunch of old WWII and Korean war vintage binoculars, and I found a pair I liked, and put it on the counter. I think he wanted $25 for them. They were in nice shape, and were a lot better than the crappy pair I had won recently at a casino.
After about a half hour, I said, "Will you take 125 for the Dan Wesson, along with the binocs, out the door?". He sat there for a while, and said, "Ok!" I ended up giving him an extra $2 I found in my pocket, for $127. I was thrilled as hell, and took the DW home, checked it out, and shot a couple hundred rounds through it the next morning. It was the last one of the four I eventually had that I sold to buy PC stuff in the early 90's, and was still in 99% condition. I regretted selling it as soon as I gave the gun to the guy.
Later on, I got my Beretta 84 at the same place. I don't remember the price I paid for it, since I bought a bunch of stuff at the same time, including a really nice German pocket knife I can't find anymore.
You had to do a lot of looking and leaving before you could get a deal worth doing. One of the local pawnshops in Vegas was insanely high, and I never was able to do any dickering at all with the owner or his son. He had some real nice S&W revolvers pass through there between 77 and 82. Several 29's he wanted as much as a new one went for anywhere else.