at Guitar Center if the box of the pedal I'm returning has been opened?
Call them. It's not difficult.
I'm guessing you're going to get store credit if anything. But yeah, just call them.
If it isn't faulty then you'll probably only be able to return it for store credit, if at all. They won't be able to sell it as new and therefore not at full price.
yeah you can get a full refund. as long as everything that came in the box is in there. manuals etc...