Quite why anyone would think a poster evidently being aware of the implications of LHS/RHS flying, time logging, knowing about "a jolly" and saying he would like to do most of the flying is someone who would need "an introductory lesson" or "is best left to someone who knows about flying" is beyond me.
If its a manufacturers demo, chances are you'll be able to fly in the LHS. If its a private sale, the Owner will likely sit LHS.
Time logging will likely only be possible if the demo pilot is a QFI.
You'll probably only get the flight for free if you buy the aircraft!