BBB - there are some craftsmen of sufficient talent, material, and knowledge who can restore certain guns to the point that panels of experts will be divided as to originality. Fortunately, most of these have high interegity and do not try to foist off their work as original - there are exceptions. Also, there are some people who will try to pass of outstanding restoration work they have commissioned as original finish.
The odds of finding an unfired 100 year old gun are small - it does happen, but not commonly. For American classics, this is a very substantial change in price. For most other guns, it simply means you have a gun of Current Condition = pristine.
I know of no way to absolutely verify that any gun has never been fired by a consumer.
