Many shops don't allow a tear down inspection. All the ones I frequent have no issue but there are many who don't.
There are so many details to absorb when looking at a shiny new gun that a person most likely wouldn't even notice a tiny barrel flaw anyhow, or write it off as a piece of lint or something.
It's important to note that this stuff happens with everything made and assembled by humans. Toasters to lawn mowers, cars, you name it.