UGH: Yes, it’s a Trapdoor Springfield, not a Sharps. Sloppy on my part.
Weaponsman has the run-down on how they authenticated the rifle using forensics, just as you would from a modern-day crime scene.
It seems to be in wonderful shape. The auctioneer seems to think it will bring $100,000-$150,000, but his estimate is probably on the conservative side since this is one of the few (if not the only) rifle on the market that can be definitively linked the the battle.