1) If they were really faked, the Soviets would have relished in proving to the world how the Americans had faked a moon landing. 2) If NASA faked a few moon landings, why would they stop? 3) The technology to fake something of that magnitude just didn’t exist in the 1960’s. 4) We left mirrors on the moon so that we could measure the exact distance from Earth using lasers. Those mirrors are still there, and if you get yourself a strong enough laser you can make the measurements as well (Lunar Laser Ranging Experiment).