4. Costs. Is the seat free, or do you expect the passenger to pay the landing fee, buy lunch, or share all costs.
Would exercise caution when advertising spare seats like this, see Art 130 of ANO, esp : no information concerning the flight shall have been published or advertised prior to the commencement of the flight other than, in the case of an aircraft operated by a flying club, advertising wholly within the premises of such a flying club in which case all the persons carried on such a flight who are aged 18 years or over shall be members of that flying club.