Obviously, there are a bunch of different answers to this question and, as someone who thinks the moon landing did happen, I'm not exactly the right person to answer this. However, two of the oddities that make people suspicious are that the original footage was deleted and one of the space walk photos was clearly an edited training picture that was taken in a pool.

We discussed this in the recent conspiracy theory post. My view is that some (maybe all) of the promotional material was faked. That might have been because they realized (or worried) that radiation (or some other technical issue) would mess up real pictures and video, but they knew the public demand for documentation was enormous.