Having run a gun shop for over 9 years, I can tell you that ALL incoming guns were removed from the boxes so that the guns serial number could be confirmed with the box and the shipping invoice, before the gun was entered into our bound book. As a result, the seals on the boxes were never intact after we went thru them. All of our 380 Bodyguards just came in a pouch with the spare mag. I don't believe they were even in a plastic wrap. It didn't happen often but we did have a couple instances, were the actual gun in the box did not match the box or invoice. Distributor reps were immediately contacted and the firearms were returned, because that meant the distributors records were likely messed up also.
As to the OP's issue. We did see some guns direct from our distributors that appeared to have been test fired more than others. As to how dirty one gun is over another, the brand/type of ammo used for test firing can make a huge difference.