I've bought 3 used guns from pawn shops. One was a super bargain, being something that I wanted that apparently nobody else wanted (22 target rifle). One was a good bargain, and one was a decent price but didn't shoot. I bought that last one on condition that it would shoot, so they took it back. I am of the opinion that if you know what you want and do your homework to know the market worth of what you want, a pawn shop is a fine place to look around. You should assume that they also know the market worth of the item. My favorite old shotgun came from a pawnshop. I was looking for a specific one and I knew that it should be worth about $200 (20 years ago). The guy was asking $250. I offered $200 and he said that "bird season is just about to start, so the gun is $250 until bird season is over, and the day after that, if I still have the gun I'll sell it to you for $200". Wellll damn...He knew the value of the gun and he also knew its probable value to me at that moment. I paid the $250, and I've never regretted it.
Do your homework. The best prepared negotiator almost always wins. I was a negotiator for 30 years, so trust me on that.