I am far from being expert on this subject but...

besides the fact that muzzle grinding is not the manner in which a purist wants his double rifle regulated, I believe independent reviews quoted in this forum showed/claimed that the Sabattis so doctored, in order to expedite shipment and sale, would only shoot with any accuracy the one brand of ammunition with which they were originally test fired at the factory. Although doubles are normally regulated with one make of ammunition, other brands of cartridges with standard loads in the same caliber will normally also function adequately. In other words if the rifling was dremeled to cause say Hornady .500 NE loads to group better, if Norma, Kynoch or A- Square ammo were substituted the results would be far less satisfactory. When barrels are properly regulated this sort of variance is not typically experienced.

All of that being said, if it helps I own a Sabatti in .470 NE with rifling that has not been visibly altered and I am very happy with it, except that the rifle is a bit light for caliber and hits hard on both ends. I am one of those that believes that if you do your homework in examining the Sabattis when purchasing, you can get a lot of gun for your money. Although I do not believe the price justifies the deliberate tampering with the muzzles, I wouldn't expect a double that retails for $5000 or so new to meet every standard of guns costing 2, 3 or more times as much. I have heard/read that Merkels costing $10K plus have a common problem with the weights/recoil reducers in the stocks coming loose from recoil and then rattling until repaired. Does this make the gun cheaply made relative to a $100K Purdey?