Given that there are spacecraft orbiting the moon today that have taken photos of the Apollo landing sites (the LEM and footprints clearly visible) it's pretty amazing that anyone still claims that the landings were fake (although I heard one claim that those were done more recently, although not being able to explain why we would have done something like that).
But the one response that I've always been able to silence a landing denier with is to ask them why - if the landings were fake - the Russians went along with it. The Russians were perfectly capable of tracking the spacecraft headed to the moon, as well as intercepting any radio communications between Houston and the Apollo/LM. The Russians even going so far as to launch a spacecraft intended to land on the moon and return a sample at the same time as Apollo 11 (it crashed on the moon).