Wikipedia:Fringe theories for dummies

Fringe theories are often discussed in Wikipedia articles, subject to the WP:FRINGE policy. Even the most radical conspiracy theories are often represented in their own articles, if they are sufficiently notable. But the problem is that they are usually written like any other valid viewpoint, and even cite some book or source as a reference. So, how do we identify a conspiracy theory as such?

A credible author that says "that is a fringe theory" is a good way to do that, but not always. Fringe theories tend to be, well, fringe, so perhaps nobody debunked it: not because it is accepted, but because nobody took the work to take the fringe theory into account and explain why it is wrong. Scientists are busy people and work on full-time important projects, they can't waste their time debunking the claims of every lunatic that shows up. So, let's see how to identify a fringe theory simply by analysis.

General form
Fringe theories may show up at any field of knowledge, and their claims would be specific to it. Still, most of them have a similar premise: they say that the mainstream description of something is completely wrong, because of some active conspiracy to keep us believing in something wrong. The fringe theory, on the other hand, comes to show us the hidden truth. Conspiracy theories provide easy explanations for things kept under secrecy, and for unknown things. They may also try to explain something that does have an explanation, but which is very complex for the layman. A conspiracy theory may even provide a self-serving explanation to use victimization when the state of things is not to someone's liking.

Common flaws
Despite their apparent simplicity, conspiracy theories usually have huge gaps that allow us to identify them.
 * 1) Logistics. Let's say that all scholars that support the "official version" are part of a secret cabal that hides the real information. How is that cabal supposed to operate? How does it reach people from so distant and different places? How do they keep contact in such absolute secrecy? How can it be so big and all-encompassing, and yet still be secret?
 * 2) The "official version" is a made-up story, but somehow it is so flawless as a story that it fools everyone who is not part of the cabal: military, law enforcement, government, media, other countries; who never suspect anything or point anything that doesn't make complete sense. Unless they are also part of the cabal, which takes us back to point 1.
 * 3) The cabal has an undying loyalty: there's never a defector that outs the cabal, its secrets and methods, even when doing so may make them rich or famous, or grant them a lower sentence if it is a criminal conspiracy that they helped to stop.
 * 4) No actual evidence of the conspiracy is ever leaked. Despite its all-encompassing reach, all such evidence is destroyed, and none is missed. Which takes us to point 1 again.
 * 5) The cabal must have a perfect system to kill any defector or anyone who discovers the conspiracy, in order to protect the secret. And that system is so perfect that all those deaths are made in a way that the subsequent investigations never discover the secret. And yet, no member of the cabal ever fears for his own security and runs to reveal the secrets to the government in exchange of protection: the undying loyalty of point 3 still prevails.
 * 6) And yet, for some reason that perfect killing system of point 5 could not stop the guy who published the book with that info, or the other guy that cited that book in Wikipedia.

Conversely, many actual conspiracies are known to have taken place; in some cases, evidence of the conspiracy, and consensus as to its existence, took years to surface. So if the above huge gaps and logical flaws are seriously acknowledged and debated, it might be that there was an actual conspiracy. Which, of course, is a completely different thing from a conspiracy theory.