It would be a very difficult thing to fake convincingly, especially back then. Anything to do with space is. (Remember Blake's 7?...).
Thinking of Apollo 13 (the movie), the most realistic sequences of weightlessness were those where they really were weightless, having taken the film unit onto an aircraft and flown parabolic curves to achieve 30 seconds or so at a time. The other 'weightless' scenes pale by comparison. And even then, you sometimes got the feeling the behaviour of the droplets of drink (for example) is a little erratic, and that the actors were having to cram a lot of activity into those 30 seconds each time, whereas the actual astronauts would have been in no rush.
The most disappointing thing about the original moon landing is the quality of the black and white tv pictures. Given that it was an astonishing achievement to get any live tv at all from that distance, the ghostly nature of the images kind of unfortunately played into the hands of the doubters. The quality of the still images still takes my breath away though.