Believer says: The Gospels are based on eyewitnesses.
But skeptic says: Well, if Mary the mother of Jesus was an eyewitness, the story of the Wise Men should have greater detail in the Gospel of Matthew. She would've known how many Wise Men there were, their names and country, and the sort of star that had been their guide, a miracle or a planetary conjunction. But Matthew says very few things about them.
In chapter one of the Gospel of Luke, the author says he learned the story of Jesus from hearsay. As for the gospels of Mark, Matthew, and John, their authors are basic mysteries, too. So it’s really impossible to demonstrate that the Gospels came from eye-witnesses.