: Pitting, it's location and how it will effect shooting, safety, etc is something someone with experience must see to judge it's traits. It is virtually impossible to attempt to explain it here, over the phone, or however.
: Pitting is rarely a dangerous thing, but can be. In Damascus barrels it can be very bad indeed as what looks like a very tiny tiny hole, may run angled, through the welds almost to the outside surface. If the bottoms of the pits are easily visible, and a scribe or dental tool can mark or feel solid steel underneath, they probably aren't a safety concern. 1 mm deep pits are 1/25th inch deep which is deeper than 1/32nd" or 1/2 of 1/16". I'd call that deep, but perception is a personal thing. To me, anything deeper than about .020" is deep.
: Pitting is something that is common in poorly maintained guns. It matters not that the primers used were corrosive. If fired and well taken care of by prompt cleaning by proper methods for the priming & powders used, the bores would be bright and shiny as many are. BTW- modern oil based solvents are not suitable for cleaning fouling left by corrosive primers. A water based solvent must be used. I have seen too many properly taken care of guns to accept a broad statement that pitting in 100 year old or older guns is unavoidable. Many have it, and many of those can be salvaged, but by someone who knows what they are doing. Many don't have any pitting at all. My own Sharps .50/70 barrel from a model 1859 has no pitting on the outside of the barrel. It was re-lined by Sharps in 1867 or 1868 and chambered to .50/70. It was only a tiny bit rough, but is bright and shiny, originally when I bought it, had nothing deeper than .001" or .002". .002 is only 5% of 1 mm. This bore polished up almost like a new barrel would appear. Polishing the lands & grooves should not remove enough metal to change calibre. If that much material needs to be removed, then a re-bore may be necessary. I know of no one who does this to doubles, but I suppose H&H most certainly will. Be aware, that if done in Engand, they'll re-proof the gun. Perhaps that's a very good thing.
: Buyer beware. I would be most hesitant in buying a gun that has pits on the outside as that was the easiest place on the gun to take care of. That would mean it was totaly negleated. The H&H you pictured or sent to me, was well overpriced in my opinion as it was very poorly taken care of and I believe poorly refurbished.
: Value is whatever you can get for something, I guess and one man's price may be well below what someone else is willing to pay - obviously.