I can only tell you about the one in Littleton, CO., which was pretty well-run, always had pretty good fair prices anyway, and usually didn't want to quibble. They were out to turn the stuff to local musicians if possible, rather than jacking everything up to stupidly-high prices because "someone on EBay paid that much!" They wait until it sits long enough to post it online, normally. I got some decent deals there just on their posted prices. For example, I wasn't going to argue with a mint condition Fender '65 DRRI with footswitch and cover for $599 when I bought it, or $110 for a vintage early-50's Kalamazoo amp in VG condition.
Can't hurt to ask, though. Just don't beat them up on stuff, if it's already fair. They treat repeat customers especially well, but if you go in with an attitude (not suggesting you would), don't be surprised if they NEVER offer you a deal.