I've watched several "unboxing" videos on Youtube where the person cuts the tape and opens the box in their living room for the first time, indicating his dealer/FFL never checked/verified the serial numbers on the gun itself.
Either that, or the dealer resealed it, as we do. Dogtown Tom is correct on every count. The gun has to be entered into the books, and there's no way I'm doing so without physically verifying the make, model, and serial number. I get dozens of guns in every day, and the check-in process is part of a workflow. I'd need a pressing reason to disrupt that.
Of course the customer can inspect it prior to doing the 4473, but I can't set mystery guns aside and leave them sitting around unaccounted for. That's a good way to fail a compliance audit.