I've got 5 GC stores in a 120 mile radius of my house, and they vary greatly in their usefulness. Evansville, IN and STL/Crestwood are both really good, STL/Bridgeton and Terre Haute, IN are both hit 'n miss, and Fairview Heights, IL is really annoying. So, I generally browse the used selection online and then go play whatever looks interesting.
My one major beef concerning all locations is their refusal to set up used instruments. Generally speaking, about half of their used basses are unplayable-rusty strings, neck bow, strings totally fretting out, covered in dust & finger goo, etc. How can you make an informed decision on an instrument (at regular/maket price also) without being able to actually play the damn thing? They wouldn't need to do a full setup-just dust it off, straighten the neck, and maybe put on a basic set of strings. Maybe this is why some of their used stuff sits there for 6 + months?