You need to give the serial number on a Parker.
50-100 USD
Value seldom exceeds 100 USD
what is the value of a Hartford double barrell 12 gage shotgun with duel over head hammers great condition
They are not marked, you can tell by the serial no. (well an looks ;)
Unlikely. Try e-gunparts.com
I found mine under the barrell. You will need to remove the wood under the barrell in front of the triggers.
No published sn data
Impossible to answer since you did not provide the serial number.
Age of the gun is important, not the value.
No way to answer without more information.
50-100 USD, 70-100 years ago