i thought of another example. "flying incidental to other business." if my friend says he wants his aircraft brought from A to B and he'll give me $100 to arrange it, i have a multitude of options. i can arrange to have it trucked, i can hire a CPL, or i, with my hypothetical PPL, can fly it there. i'm not being paid specifically to fly it, i'm being paid to arrange for the transportation of a piece of metal. legal, or not?
i'd say illegal, but technically is it?