Tons of good advice here.
I started going to pawn shops about 10 years ago. Usually quick visits over my lunch hour. As a pawn shop virgin

I assumed the marked price was
the price. It wasn't until I went with a co-worker that I finally understood the pricing game. He has a farm background and is a master negotiator. It was quite a revelation to watch, listen and learn from him.
I've become friendly with some staff at my usual stops and that probably gets me a better price. On a hot day, the purchase of a Coke or Pepsi from the 7-11 (next door) is much appreciated by the guys I know. Some people will show me what the shop has into an item, if the owner isn't around and no other customers are around.
Mostly I just ask "What price can they can do?" on an item. Quite often they will shoot me a price that is less that I the figure I had in mind.
As has been mentioned. it is always good to know retail prices of what your considering. Be polite and courteous to the staff, it goes a long way!
I found a new shop about a year ago. He puts almost all hand tools in one large bin. It's fun to see how many useful, quality, tools I can get for $5. My best so far is 23 assorted wrenches, screwdrivers, extensions and one 1/2" Gray ratchet!

I see the the occasional truck brand but lots of Craftsman, Gray, Proto, Williams, Industro, etc, etc. Some I keep, some I flip to others, some go in my swap meet box for later sales. Sometimes, I might only find a couple of tools, the owner says no charge!
Have fun!