I am skeptical about needing a Guru. Did the author of the Satcharita feel the same way, and what changed his mind?

Yes, the author, Annasaheb, initially shared a similar skepticism. The preface, which discusses his account from the third chapter, explicitly states that he began with no Guru devotion and even argued that making a Guru was a fraudulent practice, taking great pride in his own doership. His perspective underwent a complete transformation upon meeting Baba. As described in Chapter 0, as soon as their eyes met, his pride was shattered, and he became fully convinced that a Sadguru is indispensable for navigating life's journey. This powerful, direct experience completely overturned his previous beliefs about self-reliance and the need for a Guru.