"A and C", where did the above comment spring from? Have I missed something?
I find it very hard to believe that people turn up for interview with the sole intention of getting a free hours flying. Are you sure that the reason that prospective employees don't return is due to the fact that they only wanted a free flight and not the terms of employment offered to them by yourself? Personally, I wouldn't contemplate attending an interview/ working for a company that wanted to charge me for the pleasure.