Conspiracy theories are fun to read. I don't buy into most of them, but it's like reading those old bad tabloids that made claims about bat-boy, they have my attention.

Most of them can be objectively analyzed by the believability of the motive. Occam's razor/Law of Parsimony is pretty good for this. (Especially when it involves someone making money.) Most people know this and use it.

People also need to apply Hanlon's razor:
"Never attribute to malice that which is adequately explained by stupidity."

BUT, you could also say: If something is especially DUMB, like there-is-no-way-you-could-be-that-dumb dumb, then suspect malice.

It's been pretty solid in filtering the lesser of conspiracy theories. The ones that persist require a lot more of a reading investment.