Well, Twister's Pa, if the gun were mine, I'd have a tough time selling it it-I'm one of just a few "Tobinites" that seem to like the guns, this, inspite of the fact, that I've come to the conclusion that the design is totally un-suitable for modern, smokeless, high pressure ammunition. Mine gets CIP spec 16 gauge ammunition, or an occasional box of older RST low pressure stuff. I have a stash of both laid in for my own gun, which, is nearing or at the 100 year old mark.
That said, I'd price the gun at about what I think it could be sold more than once for-and, $7500 will buy A LOT of Parker, Lefever or LC Smith that at least a few more folk would would be interested in buying, let's just say far more folk than would be interested in a Tobin, regardless of grade/rarity.
"Rare" doesn't automatically make something more valuable. For what it's worth, I'm pretty sure Frank Major Tobin's personal gun, also a 12, but, much higher grade than this, sold for considerably less to one of our board members.
You are free to cough up whatever you think the thing is worth-my advice would be to make note of all the Parker's that aren't hitting their reserves at auction lately.
They are quite numerous.
Best,
Ted