Hi,
hoaxie. Welcome to the board.
haha.. should have expected that after having read the topics here for many many days. only today I noticed the question there.
Anyways, how can you be sure that someone isn't hiding something until you are that person himself??
It depends on the claim. For instance, if one claims that NASA landed on the Moon, but is covering up the existence of giant alien cities there, than one can reject that claim as
prima facie absurd unless really good evidence is provided for it.
If if you are that person, than you will always be saying that you are not hiding anything.... so thats it...
And if you are a person (or organization) who is
not hiding something, you will say the same thing. So that point is not evidence for anything.
I don't have no evidence to prove that NASA exists or not in the first place.. leave alone what it is hiding or showing off... 
If it helps, I have direct personal experience that NASA exists, having spent considerable amounts of time at various NASA facilities in the course of my work. But you can also directly observe NASA space shuttles and the International Space Station, with your own eyes. So, yes, you
do have evidence that NASA exists.
Anyway, do you wish to make a specific claim of a space-related conspiracy? In particular, do you have a specific conspiracy claim regarding the Moon?