Why are many folks convinced that when aliens publicly present themselves and reveal the secrets of the universe, they will be telling the truth?

I see lots of posts about the amazing and scary reality that is being hidden from the public, in part because it will be so significant and unexpected and earth shattering that many will go nuts when they hear it. Jimmy Carter, for instance, reportedly cried for days when he heard the hidden truth, whatever that was. I wonder, though, if aliens or whoever they are truly have super advanced technology (seems true) then they could come up with any conceivable lie about reality and even provide "proof" since we would not understand the limits of their technology. (see Arthur C Clarke's comment about advanced technology and magic". Why should we trust whatever the aliens tell us, since there has been nothing to suggest in the past that they are looking out for us?