Let's say you arrive at 11:30, as we want you there to finalize things before midnight. When we finalize your transaction, we are ringing up your Wii-U, so we need the serial number at that time. MOST LIKELY, your Wii-U will not be staring at you in the face from behind the counter. It will be out of sight, in another room, etc. So we keep a list of serial numbers up front to ring you up with, and therefore will have no idea how each box looks, which one might happen to be sitting on the bottom of a pile with 10 other boxes on top. We'll just ring up whichever one is next on the list.
Basically, at that point is when you want to ask if they can take a look at the individual systems and that you want one in the best condition. Let them know you don't want one on the bottom of the pile. Just don't be the last person to pick up your Wii-U! Typically this would be later on launch day or the day after, so you shouldn't have to worry at midnight.
This might seem like too specific of a request, but I have had damaged 360 and 3DS boxes, including limited edition Call of Duty 360's or the Zelda 3ds. So it can be a concern if you care about such things.
Thanks for the info. Anytime I buy something I look at the condition of the box before purchasing. That way you can tell if the product was mishandled.