Commercial air tour
The FAA may consider the following factors in determining whether a flight is a commercial air tour:
(1) Whether there was a holding out to the public of willingness to conduct a sightseeing flight for compensation or hire;
(2) Whether the person offering the flight provided a narrative that referred to areas or points of interest on the surface below the route of the flight;
(3) The area of operation;
(4) How often the person offering the flight conducts such flights;
(5) The route of flight;
(6) The inclusion of sightseeing flights as part of any travel arrangement package;
(7) Whether the flight in question would have been canceled based on poor visibility of the surface below the route of the flight; and
(8) Any other factors that the FAA considers appropriate.
Source: 14 CFR Federal Aviation Regulations §110.2