Does the pilot make money on a cost-sharing flight?

No, never. That's the very principle of cost-sharing: the pilot shares the real costs of the flight, pays their own share and cannot make any profit. If they made a profit, the flight would no longer be cost-sharing but a commercial transport service, which the law prohibits in this context.

How Volara guarantees this

With a fixed contribution, the amount per seat is capped at the share of a single occupant, that is, the direct cost divided by the number of occupants, including the pilot. With an equal split, the costs are divided between all occupants and only one booking is accepted per date. In both cases, the pilot never recovers more than their share of the expense.

And the service fee?

The service fee you pay goes to Volara, never to the pilot. It's added to your contribution and doesn't change the fact that the pilot, too, covers their own share of the costs.