Depending on specific national laws of some countries, generally speaking, a private pilot can operate an aircraft as pilot in command, provided that the operation of the aircraft is not commercial, that is, no charge is made for the flight. Example is an aircraft salesman, demonstrating an aircraft in flight to a potential client. His salary should not be derived from flying, nor should there be any charge to the customer for a flight in that aircraft. Company goods or personnel can be flown in that aircraft.
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I have known an aerial photographer who has a PPL, who rents airplanes to make pictures of estates for sale. He does not derive his income from the flying of the aircraft, but from the aerial pictures he sells to real estate companies.
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A PPL holder can share the expenses of aircraft operations (with passengers) if the aircraft is not operated commercially -
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