I've had good experiences with the Manchester, CT, store. I usually buy inexpensive stuff like used effects and cables.
I did buy a Roland Juno 106 there that I checked out thoroughly to make sure it didn't have any bad voice chips. I put it on layaway and came back the following week -- they told me that they checked it over again after it warmed up and one of the voice chips was bad. They even offered me some money off if I still wanted it. I really appreciated that.
I was in the West Palm Beach store a few months back (seems to be an awful lot of complaints about that store) and one of the guys behind the counter was trying to sell a customer "premium" USB cables -- told the guy it would make the sound coming out of his CD decks so much better. That kind of thing really pisses me off.
I always know what I am buying and what it is worth. They have decent deals on used stuff and that means that they likely low-balled the original owners. Fine with me. I will never sell anything to them, I can do just fine with Craigslist or eBay.