It seems to be an article of faith among conspiracy theorists that their critics have no way to determine the credibility of the conspiracy sources. That belief will not be true for all (or even many) critics. In fact, people drawn to the debunking of conspiracy theories generally arrive there because they actually know something about the subject from professional or similar experience. And it is not necessarily a categorical rejection, such as not accepting sources associated with well-known tabloids or self-publishing platforms. It is most often a substantive rejection because the critic really does have the knowledge necessary to test the correctness of the proponent's source.
A similar article of faith seems to be that critics have no way to determine that the conspiracy theorist herself doesn't know what she's talking about, leading to comical examples of bluster and gaslighting. Yes, we can tell when people are lying. Most conspiracy theorists are blissfully unaware just how dumb they sound, especially when they're trying to be self-important.
Indeed, what conspiracy theorists, armchair detectives, and other self-appointed "investigators" dread most is people coming along who actually do have expertise and actually do know what they're talking about. The armchair duckies can't compete when it comes to actual knowledge and understanding, so they have to make up new ways in which they're allegedly superior, such has having some sort of innate, natural understanding, or an unassailable personal background. Here, actual expertise and experience is being dismissed—with considerable and fervent hope—as "snobbery."
No, it's not a cultural thing. No, it's not an elitist thing. We simply require a demonstration that sources purported to be authoritative have some foundation of authority. In the real world, the celebration of mediocrity and ignorance is not really a thing.