Value is all in the details when it comes to Parkers. The things to consider include hammer/hammerless, Damascus/fluid steel barrels, the grade, the frame size, barrel length, whether any modifications have been done, the amount of case color left on the receiver, the color left on the barrels, and so forth.
Here's the writeup out of the Blue Book of Guns.
http://doublegunshop.com/bbp3.htm
Pay particular attention to the following:
"A Parker IS NOT 60% if the barrel bluing and stock forearm varnish are 60% but case colors are only 10%. Typically, a 60% case color Parker shotgun will have 90%+ blue and varnish, yet this does not mean the gun is 90% overall. Similarly, a 20% case color Parker will probably have 90% barrel bluing remaining.
Strong, original case colors are the key in determining Parker condition and subsequent values."
Parkers run from about $400 to $100,000.
A common 12 ga. VH, the biggest selling model with about 79,000 made, could run from about $500 to $3500, plus more for ejectors.
My uncle just sent word that our relative's collection is to be auctioned off in February. I'd love to buy one or more, but I'm extremely hesitant to get involved with only a little knowledge.
John