My instructor never asks before he touches us to correct, but his corrections, when given, are always appropriate and helpful. I do get a little embarrassed when he corrects me as I am sensitive to criticism, but I know he is trying to help. Normally he corrects the newer people to his practice more than I am corrected, but he also does more of that when the class is very small. For example, today there were only four of us, and he corrected me several times, but he also praised me at least as many times. I try not to take the corrections personally, though sometimes it is hard not to!