no, you couldn't tell if its "new" or been on the floor for a while, if it's taken care of at the store. That is a cab just shipped to the store will look like one thats been sitting there for 6 months, except for maybe some dust. unless something drops on it and you see visable damage it should be fine. you can always ask for a boxed one, or order one.
but i just got my 2x12 shipped to GC by UPS... and UPS f'd up. soemthing fell on the box, and now there is a tear in the grill cloth and dent in the side of the cab... now i have to get a new one from boogie.. how ever long that takes (but i get to use the one i have now in the mean time)