I've found pawn shops to be a pretty good source for guns in my area.
Like others here, when possible, I'll make a regular loop of shops. You never know what will show up.
In addition, if you're a recognizable face and develop a relationship (or at least are pleasant) with the owner/staff, they'll look out for you. The brother of one of the owners of a local shop was getting rid of an AMT 1911 Government Model (which ended up being an un-fired safe Queen) which I picked up for a good price. The PS owner knew nothing about the gun but since he knew I was in the market for a Hardballer Longslide, he asked if I would be interested in the GM. I use it in IDPA competition.
I picked up a drawer worn S&W Model 19-2 (1970 vintage) with a 4" barrel for $200. Although it doesn't look good with the bluing polished off the cylinder, it is very tight and shoots great. I couldn't be happier with it.
I don't like to dicker. If I have cash, I'll ask "Is that your best price?" If it's still too much, I'll respectfully pass. I have managed to get a lower price that way and I don't have to haggle (I REALLY dislike haggling).
If they have something I want and I'm short of cash, I'll let them know. I'll pay the asking price (if it's in my personal "reasonable" range) and then put it on lay-away. I figure full price is my cost for the lay-away. But, at least that way, I'll eventually get a gun I would have had to pass up on otherwise.
Basically, if it seems to me that a shop owner/staff are jerks or not interested in my business, I'll cross them off my list. I'll spend my money with folks I like dealing with.
I keep in mind that the pawn shop is in business to make money. I'm not trying to take food out of their mouths, but I also don't want to pay for their kid's Ivy League education.
Matt