In reply to John Stainforth:
> Way better to appear rude than allow an accident to happen. If the people in question are obviously beginners, and you are experienced, I think you almost have a duty to come to their aid and educate them ("mentoring").
I agree, there are ways and means of telling people considerately, rather than officiously. I often used to talk nicely to people at SS if I saw a set up which was either dangerous to them or harmful to the rock. Pretty well all were grateful for the advice, and took it in good spirit.