This is always going to be the problem with non instructors effectively teaching (regardless of what you actually call it). In an instructional relationship the commander is the Instructor and the student expects to be briefed, debriefed and generally nudged. In a more loose arrangement you have more of a problem with establishing responsibility.
It sounds to me like you are entering into a teaching relationship without the background to maintain command ofnthe situation but allow the student to develop.
As was said earlier, you really need to establish who is in command first. Make it clear that the person your are checking out is in command and that you will be doing nothing to 'nudge' them and that after the flight you will discuss with them if the performance was good enough to be let loose.