"Once an author writes a book they are considered an "expert" on the topic."

So, if I write a book about the Moon being made of green cheese, I am an expert on the Moon?

Just proves that labels mean nothing. That just because one is called an "expert" does not automatically mean they know what they are talking about and that they are right.

Relying on such labels is a logical fallacy. This is called 'overreliance on authority'. One cannot take the word of "experts" for granted. One must look at the evidence itself and judge accordingly.

Brian