CAR 2 (definition of a private operation) and CAR 206 (commercial operation) are you "go to regs" for these questions. Lot of old wives tales get out regarding private ops. Basically what has been said here is correct, equal cost sharing ( I would be leaving out anything apart from a direct cost ie fuel, airways, maintenance) don't advertise and most importantly not available to persons generally.
You can unnecessarily create grey areas if you venture to far from the above