It would've been so easy to lie to the public back then. Tv and radio was the only source of news/information. How could we no for certain they were actually there..... And then there's the story about the lost / overwritten tapes. I don't think I buy it anymore
We know for certain that they had the capability to send people to the moon and back because they showed it off to anyone who wanted to see it. It was a secret before. It wasn't a secret afterwards. Quite the opposite.
We know for certain that a very large number of people were involved, many of whom had enough relevant knowledge to judge whether or not the kit they were making was up to the job of taking people to the moon and back. We know that none of them have ever said it wasn't.
We know for certain that they sent missions to the moon at the stated times because they were broadcasting and numerous people around the world tracked the source of the signal, including numerous independent people. You could detect the source position of the signal using publically available equipment and many people did. To the moon and back.
So what purpose would they have had in developing the tech needed to do it for real, spending all the money needed to do it for real and then spending more money in taking the huge risk of faking it?
That's assuming you accept that they could have faked it, which is at best debateable. No CGI in those days. Consider, for example, the pendulum video. How could that have been faked with early 1970's technology?
We also know for certain that the government of the USSR accepted that the USA had beaten the USSR in the space race. Bear in mind this was the height of the cold war and the USSR and the USA were in bitter conflict over pretty much everything, including proxy wars in which many people died. The idea that the USSR was in on a conspiracy to pretend that the USA had beaten them in an important and extremely high profile thing is really rather implausible.
The conspiracy belief is hugely implausible. I don't buy it. Not at all. Not for a bent ha'penny. The idea is hugely implausible and has no sound evidence behind it.