I used to hit them all the time, when I had cash flow. I got some really nice deals out of them too. An older Colt 1911 Series 80 for $450 w/ box, a LNIB S&W 686-4 $350, a S&W M-P9 w/ nite-sites for $350, among others.
I find that you gotta go to these places, kinda establish a pattern, talk shop, if they are a chain learn their date codes, etc. The pattern works because even if you dont buy anything, they recognize you. Talk shop because they are just like any other retail employee, they have bad days too, and would love nothing more to vent, plus you learn that company's inner workings. Learn those date codes. The dates in which the product came in and when it was put up for sale, that way you can stuff like "Well I know you've had this since March of last year. If you wanna sell it so you can get some cash and clear some shelf space, here's my offer.". Oh, and dont hesitate to ask if they have something in the back they dont think they can sell, like a broken gun, I got lucky and one shop did. I paid $105OTD for a "broken" Marlin that was reassembled wrong.