So Sagan thinks appealing to authority of consensus is fine, but not authority of someone in charge?

It's still not clear to me exactly what sorts of authorities we can and cannot appeal to, and why one sort is fine and another sort is not.

And what about authority of a cop (i.e. someone in charge)? If the cop tries to pull me over, am I free to ignore him because he's not a scientific expert, thus he cannot appeal to his own authority?