No matter the make, the brand value etc, a polished off patina disqualifies it. Nothing is more beautiful (to me anyway) than that matt grayish surface when the case hardening has faded. Nothing more barbaric than an old gun buffed bright.

As for the other bits- always check the ribs, the bores, the function and feel of the locks (especially in hammer guns) and signs of insensitive treatment/repair such as buggered screws and polish worn corners in eithr wood or metal, and rust. Well used guns are not allowed to rust.

The late Geoffrey Boothroyd mentioned the smell of a well used old gun. He had a point.