Many people say foolish things with so much conviction, they convince people what they're saying isn't actually so.
It's almost like they believe their own BS (unfortunately, some actually do).
Learn to see through people's false bravado and dissect what they're saying for what it is.
When it comes to one's ideas, it's foolish for people to ask "credentials" of him or her. What were Socrates' credentials?
If the idea is sound, the source is secondary.