Yes. Walk in there, don't dress like a hoodlum, don't wear a backpack, etc. You're already on their good side if you can do these things. Say how's it going, tell them what you're looking for, don't just go wandering around. Don't tie up their time, they have other shitballs about to walk in the door they don't want to deal with.
They aren't going to haggle over a few bucks, that'll just annoy them. Don't even try it on something under $20.
Say they have what you want, and it's $100. If $100 is a good price, be fair about it, and just pay. If you really do think it is marked up a bit high, never try to ask for more than 20% off. Also, never ask for less than 10%. Don't get too excited about what they show you or point out to you, then you look like a sucker who will pay full price.
"This yaddayadda looks kind of worn here around the blahblah, do you offer any sort of guarantee on it?"
They'll probably say no, most don't do anything much more than a 24 hour return, if that. Pawn shop employees are smart about their inventory. They know about the warranty of items, especially tool brands. They might mention it to you if they want to sell it. If they want to sell it, they'll work with you
Just follow up their explanation with something like: "If you could do $80 for me, I'll take it right now, then I don't have to worry about spending more mailing it in for replacement later"
Most importantly, whether you buy something or not, say thanks a lot and say you're going to check them out again sometime. Two things stick out in pawnshops. Good customers, and bad customers. Finally, if you become a repeat customer, don't go in there haggling all the time, that's the fast track to bad customer.