As far as tolerating debatable surface issues, or being more lenient on a decent looking coin with a relatively minor issue as market acceptable enough for a straight grade, mainly?
This isn’t old old copper, but a borderline coin with decent eye appeal and nice color. I had a feeling there was a strong likelihood of coming back details but I wanted it in a slab anyway. Sure enough, AU Details - Obverse Scratched last week if that helps at all with getting at least some idea of the current threshold.
I tend to think, yes, NGC is more lenient in my personal experience. Not lenient with grade, but with slight problems. I have had NGC straight grade early copper that had minor cleanings, small scars or scratches, and light environmental issues. These are large cents and half cents I'm speaking of, specifically. Additionally, I've had a couple PCGS "questionable color" Indian cents and Lincoln cents straight grade at NGC. I almost always send my copper to NGC these days, and my classic silver coins to PCGS. IMO, PCGS is more accurate on classic U.S. silver issues, plus they bring stronger prices when selling.
Same. There's individual examples that will show anything, but overall I find them more lenient as well.