Interestingly, Jesus has an answer when asked the same question. Jesus said, "By their fruit you will know them."
Or as I like to say, quoting my own authority, "The proof is in the pudding."
Another quote you can take to the bank is "How is that working for ya?"
Unitarian Univeralists covenant together to affirm and promote seven principles the fourth of which is "the free and responsible search for truth and meaning."
The ultimate authority is, of course, one's own conscience assuming one's conscience is "informed" and authentic. People we have learned from cognitive science are subject to "confimation bias." So doubt is the spice of life even doubt of your own beliefs.
So when I suggest questioning authority, I am including one's own, but as Plutonius says in Shakespeare's play, Hamlet, "above all esle to thine own self be true."
As Socrates said, the hallmark of a wise person is knowing what they don't know. So, another one of my guiding principles is "Don't believe your own bullshit because it paves the well to hell."