Good advice 4x. I did something similar on one of the blitz tours on HID. Had pax helping unload the cargo and heading back and forth to the fence. Told the FOI that I needed to supervise the pax and that he was welcome to look around the outside of the aircraft in the mean time, until I was finished.
I then placed all the legally required documentation (lic, medical, MR etc) on the seat and told him that all the legally required documentation for a charter was there for his perusal.
It was after that that he wanted to look in my navbag (as mentioned earlier) that I declined his kind offer. All done politely though and no problems.