You can ask him to think about the cold war. The soviets independently confirmed the flights of Apollo 8-17, they were listening intently. If there was doubt about the legitimacy of the program, they would have been shouting from the mountaintops. To believe that the Apollo program was all a ruse, you'd have to believe the same about the entire cold war. The tensions with Cuba which last to this day, the Vietnam war, the buildup of nuclear arms - was all of that a sham? In that case, this ruse would have come to encompass so many hundreds of thousands, if not millions of people, that there is no way that a secret like that could be kept for 60+ years.

Shorter answer: the Apollo astronauts left mirrors on the moon. Shine a laser at that spot, it shines back. Shine a laser elsewhere, nothing.