I treat all my red letter days, birthday present flights, and similar as real trial lessons. I try to persuade everyone to have a go on the controls, even if they hadn't planned to in the beginning. I telling them they may never get a flight in a helicopter again, they ought to at least have a try, and not to worry, I'll take over if they don't like it. A basic briefing takes very little time, and I give a bit more detail during the start-up etc. Almost everyone has been glad they gave it a try, and some really want to carry on, even if they had no intention of doing so before. If they don't like it I take over, and I think they learn quite a bit ust by watching anyway.
So why doesn't everyone do this; it's really no more difficult?