I completely agree with canvasback, condition and originality, while sometimes related, are not the same thing. My interests for collecting and shooting primarily are British and an occasional European double. I grade guns by .....
Original quality
Current condition.
Sometimes brand recognition, provenance, rarity or unusual features come into play.
Originality to me is mostly one indicator of the amount of use, abuse and past repairs and can be useful in judging the useful life left in a gun. By itself it does not affect the way I value a gun very much. To me and a lot of other serious double gun nuts the vital part is the barrels. Some faults here can be corrected properly by one of the handful of truly qualifyed double gun specialists in this country but many of these repairs can cost more than the value of the gun. For example, relaying a loose rib can run $300 to over $1500, sleeving is $3000 plus now and generally does not add that much value to a gun except in very special circumstances. New barrels? Try $8,000 to $12,000! For myself personally and many others I know, the issue of proof and barrel wall thickness is a major factor in the value of more expensive guns. Unless a gun is in proof and has decent wall thickness I won't normally pay over $3000 no matter what the gun is. I may have missed out on a few fine pieces this way but I haven't been stuck with something that I can't move along when I tire of it. Remember, the value of any used gun is only speculative until it sells, only then is the true value established for that particular gun. Asking prices, advertised prices, auction estimates are only a guess, not true value. And yes, originality definitely does affect values on some guns, very little on others.