Perhaps the previous owner shot a different barrel and then reinstalled the factory barrel when selling.

If it shoots well, the barrel nut is tight, and you are not getting any signs of headspace difficulties, I'd go with it. Bottom line with me is whether or not it shoots accurately.

Having said all that, if you have any safety worries, it is absolutely worth the peace of mind (piece of mind? ) to have someone you trust check it out for you, especially if that is something you are not comfortable doing yourself.