Standpoint...how much of a hit does a refinished gun take ?

Depends totally on who does the work. Folks like Turnbull or work done by Guild members holds it value much better then someone not known. Far as actual percentage drop, it depends on the rarity of the gun to start with IMO.

Shouldn't a restoration be somewhat undetectable? I would think if restored to original condition? Buyer should ask questions as per work performed--only if honesty prevails?

Not a collector, just another point of view: I sent some Missouri wood and a well-used Parker VH with little checkering left but essentials unbuggered to Chris Dawe to make it look better. What I got back was worth several times what I paid for it---what this unsophisticated gunner imagined as original.

A refinished gun is not a collectible gun to almost all collectors. You can’t decide what is original and what is redone and original condition is one of the key things collectors. That’s not to say a well done refinished gun does not have a market but just different buyers as a rule. If it is rare a collector might buy it anyways until they can find a non refinished example just to fill a hole in their collection.

As to price it comes down to how good the work is. A nicely refinished gun should bring 80% of what a non refinished gun in the same condition and a refinished gun can never be 100%. It’s refinished so I put the top end at 90-95% max.

Some guns are so often refinished like Model 12 & 42 that all high condition and all high grades must be examined with extreme care. Some refinisher are as good as the factory ever was. But the telltale signs of wear, of polishing and of upgrading can be seen if you know what to look for and pay close attention. My favorite are the guns upgraded with features not available for a decade or more before the serial numbers. Winchester did not pull guns out of sequence and store them for 10-15 years like one seller tried to tell me.

I think jOe's question is a good one and since I have a stake in this issue I'll give my opinion which is I have no real opinion .

I'll give a general statement that pertains to Parkers. Anytime you restore a graded Parker you reduce the value EXCEPT if the gun is in such poor original finish that it looks UGLY! The gun that I will show is a Parker AA hammer gun (I think there were 5 made) so it is a very rare gun.

The first picture is what the butt stock looked like when I received the gun (really nice huh!). The finish was so dark that the figure was not visible. the second and third pictures show the same butt stock with one addition that the client requested. The client wanted a skeleton butt plate installed. It was not an ordinary butt plate however, it was a cut-off from a Parker AA that he had.
https://imgur.com/MG9HL7n
https://imgur.com/h09YD6a
https://imgur.com/5dhv7Rw

Doug, you do some beautiful work, definitively worth more now!!!!

That's part of it, too, gunny---the pride we take from a craftsman's work strengthens value of our guns, collectors, graded or not.