Justiciar
if A (client or customer) pays C (employer) so that B (pilot) makes the flight
As you have put it, I totally agree. The key, IMV, is that the pilot must not be obliged to fly.
However I think it would be pretty unusual if one of my customers actually specified that I FLY to see him
One situation which I didn't get into was when a customer once asked whether I could take his son up for a flight. Before FNG gets all worked up about this

, such a variation isn't that uncommon, and CAA's view would be the last of my concerns; it would be the insurance. In the end it didn't happen because the customer felt he would fall foul of his company's rules on gifts