Not sure how new you are to guns, but bear in mind that along with the price of a gun at your LGS comes a lot of experience and friendly advice. Finding a gun store (whether LGS, pawn shop, whatever) with knowledgeable friendly people can be worth a few points against the price of a gun. If you have no questions to be answered and don't want to fondle the actual gun you're going to buy then by all means, save the coin and shop online, just factor in any shipping and ffl transfer costs.
That said, we price our used guns at what we see actual online used sales on same item happening. Not what someone is asking but what they're actually selling for. I wouldn't dismiss out of hand the LGS's of the world for used firearms. Personally, I can think of three whole guns I've bought new. One I ended up reselling as I didn't care for it, one is a black powder rifle I still have and a 9mm Extar that is simply not sold through stores and it seems like owners never part with. Having been in the gun selling business since he 80's, I have found that I like saving the money by buying used guns in good condition. I started my relationship with a LGS when I moved from NJ to Fla and, over the course of years, got some very sage advice. There was no internet back then, but with much that one reads on the 'net it must be taken with a grain of salt the size of a mid sized SUV.
I think you might be doing your local guys a disservice dismissing them out of hand on used guns. Even on new guns that might cost a bit more from a LGS as opposed to online the pre and after sale assistance can be worth a good bit. YMMV.
