They say, "How can you trust the Bible?"
We say, "How can you trust the “big bang” theory?"
Second hand is not always out of hand. In Luke 7:18-28 we see the imprisoned John the Baptist wondering if he had understood Jesus rightly about His being the Messiah. Jesus doesn’t speak to his emotions (and John was family), Jesus sends John back to the Scriptures (Isaiah 35:5-6). Jesus provided reassurance, but notice that this would be faith in the report of others.
You can’t just say, “Well, men wrote the Bible, therefore it must be flawed”, because if the claim of the Bible itself is true, God can get men to write what He wants them to. It is not self-refuting to claim that men wrote the very words of God and that it is inerrant. If that is your problem with the Bible, get rid of every book that you have because every single one was written by men. You can never trust anything else that you ever read in life. Face the fact; you trust much of your life to second hand knowledge.
Be grateful for Luke, and the “second hand” of the Holy Spirit (2 Timothy 3:16-17 / 2 Peter 1:20-21 / 1 John 4:13).