In my heydey, I bought, traded, and sold a lot of handguns. In some cases, I would buy a handgun at one dealer, and trade it on a different handgun at a different dealer before I ever fired it. Was that then a used gun? It was owned by a private citizen (me) but it was unfired. (Why did I trade a gun like that? In some cases, I got a great deal at one shop, and then found a gun I wanted more at a different shop, and the second shop gave me a good trade since I did a lot of business with them.)

I often saw guns I had traded in, unfired, in the dealer's case marked as new.

As for S&W not cleaning guns after they are test fire, I can confirm they do not. I once asked why they didn't, and this is what I was told: when the gun is finished being assembled, they test fire it to make sure it is in working order. If they disassembled it to clean it, they would have to test fire it again after reassembling it to re-certify it as in working order...so, they don't.