Buying anything used is a gamble for sure. I saw an AMAZING special on TV last year. A classical violinist owned and played a Guarneri - I believe early 1700s??. About a 2 - 4 million dollar axe depending who wants it bad enough. Anyway a computer sound engineer in the UK bet him he could build a replica that not only HE the owner could not tell was fake by playing or hearing it!!!! Of course the musician said BS!!!! The special then gave a history of Strad and the Italian makers and the forest of sound where all the wood STILL comes from to this day! Fascinating show. In the end - the musician barely - barely was able to pick his axe from the repop. He admitted really when it came down to it - he took his best guess. The engineer uses computers and his own software to analyze the sound - of course the wood thickness etc. It took him 6 months but he made a 1700s violin that would basically fool anyone in the world. NOW - he admitted that even if he were unscrupulous 2 Million would have him loosing money on making it. I forgot how many hours he and his team put into it.
On the Bess I bought - up front I am always BS - its 100% wrong - then I have to prove everything is right. I have put in probably 60 hours in this one gun so far - before, during, and after buying it. I have analyzed every screw and piece under 4 light wavelengths and used 800x magnification on the wood and metal. I have sent photos to some of the best Bess and gun guys in the world - so far - 100% legit across the board. I bore scoped it multiple times and its exactly as I would expect. The vent hole is lightly used and not shot out leading to this gun probably not being a service weapon. It is possible the lock did not originate with the stock - maybe - the only reason I say that is the placement of the vent whole in the pan; its right, good, but not perfect - maybe a little to far to the right for my tastes. But these guns were hand made and were being adjusted via trials. The lock itself is 100% genuine. The stock is 100% as it should be.
Unless there is an exact way of knowing 100% a 1st model Bess is or is not 100% original - I would have to say this one is. Its not perfect by any means - the butt stock has ancient repaired cracks, I am about 99% sure the ramrod is a very well made replacement, and the barrel proofs and regimental markings are very, very faint - just worn from rubbing. It has reg markings on the barrel and I keep trying and trying to pencil rub or charcoal rub enough to get an ID - but alas - only time knows.