Speaking from a shop point of view, there is no way we can sell an air rifle or air pistol in a sealed box. We have to check them over and record the serial numbers (you would be surprised how many times serial numbers get mixed up on boxes). Companies like Weihrauch also send their guns in empty, so we have to fill them and check they are holding air.

It has to be a big shop to hold stocks of unopened guns for every gun they have on the shelf as well (space being one thing and the stock holding money as well).