In the second case it's flight sharing and the pilot would have to pay his share of the direct cost of the flight.
Not sure this is correct anymore John. I believe that the pilot simply hasn't to make a profit for a flight nor can the passengers pay towards the cost of any servicing whether scheduled or not. So basically if a mate asks me to fly his wife and himself to France for a holiday and pick them up in a fortnight then it doesn't have to cost me anything at all, they can pay all of the rental expenses.