I agree with all that has been said so far.
Here's a couple more to think about.
1. Someone rings up and asks for a trial lesson for their spouse and 'by the way could two other passengers sit in the back?'........in other words the intent to fly 3 people was there from the outset.
2. If a friend asks me to fly them on a 'jolly with their missus' and I still sit in the right hand seat and 'teach' is this flight legal?
The point I am making is that in each case these flights are booked and agreed in advance, does this make them any more 'grey' than if they were spur of the moment.
As an instructor if I invite the trial lesson students partner along then I see this as quite OK but if they ask me in advance I am not sure what the answer should be.
Confused? <img src="confused.gif" border="0">
JWF