I would say whether a book is to believed depends on the contents. Sherlock Holmes is fiction. I believe the Bible is a true historical record of God's dealings with mankind. For anyone to believe this would mean more than a casual look at the Bible. Millions have made such an examination and are convinced the Bible is what it claims to be, "not..the word of men, but, just as it truthfully is..the word of God. (1Thessalonians 2:13) Millions of thinking people.
Argumentum ad numerum. Millions of thinking people have done the same with the Qur'an. Millions of thinking people have done the same and rejected both books.