People can and should work together, then they should divide the output according to anegotiations before. Renting a human is as wrong as owning one.
If a child offered to shovel your driveway you should negotiate the price for the whole job. You SHOULD NOT pay him according to how long it takes. That would be renting a human, which would be slavery.
But if you don't know how to price the whole job, an hourly wage is less risk! If you price a whole job wrong you could lose money, or at least end up earning less than you would at an hourly rate.