I guess a gun is worth what someone is willing to pay for it.

This is what makes buying and selling these old guns a gamble, and provides some of the joy of doing it. :D

"Need another shooter?" I have a shooting collection and I have "needed" another shooter about 200 times over the last 60 some years, and that's just the Parkers.

My advise: Offer what YOU think the gun is worth to YOU. If the seller won't settle pretty close to that, walk! They can't eat you for offering. If they are insulted, well, sorry!