I buy guns on a regular basis from all of the SE PA shops that have been mentioned so far on this thread. I'm a little older than you guys and probably have bought a lot more guns, so let me give you a quick analysis of these three shops.
Dimmig's Gunshop (On Route 202 in Chalfont, PA)
Larry can come across as a bit of a jerk until he gets to know you, The running joke is that when he's pleasant, he must be taking his meds.
That being said, he has a good selection of product that is a bit more on the uncommon side. His prices can be on the high side, but if you are a real buyer, and pay by cash or check, he will work you a deal. Once he gets to know you a bit, he's a lot more friendly to deal with.
My last stop there I picked up a S&W 610 (LNIB) and a A-prefix S&W Model 41, for just over $900 OTD. That's about $100 less than what would be considered a good price for the two guns. So he's willing to deal hard on used stuff once he knows you.
Surplus City
Bunch of nice guys. The shop owner (Rob) is a little brusk, but a straight-up guy. Prices are good, and they stock the cheap Century stuff, like the SAR rifles when they were available. I've bought a bunch of C&R stuff from them, often for less than Century would sell to me direct for. Rob's brother owns Phoenix Distributors (which is actually located in the same building) and they bulk buy from Century and do a lot of used PD guns. Phoenix retail sales go through Surplus City, in general, though they are a regular at gun shows. I haven't bought anything recently from them, primarily because they haven't had anything in stock I was interested in. I did get a good deal on a police recovery S&W 629 from Phoenix at a gunshow back in September.
Tanner's Sport Center
A big shop with good staff. Both Ray's (Senior and Junior, the shop owners) are good guys and willing to work a deal with you. Their markup is reasonable on the large new gun inventory (~ 15%), and they have great deals on used guns. They get to know their customer's, and it's not unusual for me to get a phone call from Ray or one of his staff to let me know something has come in, new or used, that I might be interested in and asking if I want them to hold it for me. They stock AKs and AR's and often have interesting black rifles (a Galil a couple weeks back, an NDM-86 on the rack right now). They will definitely work on prices with you, and they turn over a lot of guns, both used an new, so regular visits to the shop can turn up some interesting stuff.
There's also a little shop up on 313 in Dublin call Quinby's. They are mainly a shotgun/hunter type place, but good deals can be found there on used guns, and when they have EBR's the prices are right.. About a year ago they had a preban AK on the rack for $550, and I picked up a basically new NHM-91 from them for $400 OTD.