I only walk roofs that I feel safe on, generally that is single story less than 6/12 pitch. Most shingles here are comp. If questioned I tell clients I do not make this determination until I see the roof personally.
I have in the past had that terrible experience of sliding down a roof that was too steep that I knew I should not try and get on and luckily caught the ladder.
It will NEVER happen again, No inspection fee is worth risking my health/life or my time with my wife and kids.
I agree with those who have stated that most of the time you can identify defects from the gruond with the proper equipment as well as walking the roof. Sometimes areas are not visible. I note such and move on. Occasionaly there are designs that there are unviewable areas that I really would like to see and cannot. Unfortunately that is life and I properly note it and recommend further or annual review if the situation warrants.
I have lost a couple inspections over the years when the client discovered I was not going to repel down the roof for them. I gladly told them good luck and went on my way. My health/life is worth infinately more to me and if someone else is willing to risk theirs - that is up to them. Those seem to be the exception and most of my cilent have no issues with my proceedure.