Ah fair enough. Could I suggest the following conversation then -
Pilot - I'd love to take you to Exeter. It's just a shame the landing fee's so expensive
Passenger - Oh thats OK, I'll pay for that
Pilot - Oh thats very good of you.
Job done !
Erm, no. Job not done.
Pilot - Oh thats very good of you.
The pilot needs to either split the costs equally or absorb the lions share.
Also, the fact you were leading the horse to water on the landing fee front might be frowned upon a little, since you were making the payment/contribution of landing fee a condition of the flight.