Here is the section in full from CAR Part 61:
a current private pilot licence authorises the holder to—
(1) act, but not for remuneration, as pilot-in-command of an aircraft of the category for which the licence is granted, and for which the pilot holds a type rating, and that is not operated for hire or reward, and to carry passengers in that aircraft;
When boiled down the essense is that the pilot MUST pay for a minimum of 50% of the cost of the flight. The problems arise when some sort of barter takes place that may or may not be traceable should the CAA investigate. I thought of a relevant example in my case. If I was to fly Susan and another couple to Wellington for a rugby game and I pay for the flight but they buy me my ticket and/or take me out to dinner afterwards, surely that is a reward? I know that the CAA is being more active in investigating people who allegedly are dodging the law and I am worried that I will inadvertently get into trouble.