And why assume the other is lying? This Ask HN is specifically about passive income, and calls for people to share their profits. It's not about them posting their IRS returns or other proof. If you're gonna doubt them, might as well skip the whole post.
At worse, what you describe is a snake oil sale.
But people can genuinely learn things from this or from Tim Ferris work too, so it's more like any self-help book/product sale basically. As long as it contains useful stuff that the buyer didn't know before on their own, it's legit for me.
Of course if the content is good, it still relies on the determination of those applying it. And some luck besides.