Pitch fees are paid before trading. A festival charging for the spot, a market charging a percentage and a private booking that pays a flat fee are three different economics, and lumping them together hides which events actually pay.
A booked Saturday cannot be sold twice. Deposits and clear cancellation terms are the only protection against a date that disappears two weeks out, and a handshake booking is not a booking.
The vehicle sets the ceiling. There is a fixed amount of storage and prep space, so running out at two o'clock and throwing food away at six are the two failure modes, and both are forecasting problems.
Events differ wildly in profit. A busy festival with a large fee can earn less than a quiet corporate lunch, and only per-event figures — takings against pitch, staff, stock and fuel — reveal which invitations are worth accepting next year.