The author admits to being 'mischievous, talkative, cynical, and critical' with a 'logic-driven mind.' Why should I trust a narrative compiled by someone who was admittedly arrogant and prone to argumentation, especially when the text itself warns against such a mindset?

You are correct to point out the author's description of his former self. In Chapter 2, the writer, who would be named Hemadpant, openly confesses his initial character flaws. He describes himself as having been 'mischievous, talkative, cynical, and critical,' and 'always proud of his own wisdom.' However, the narrative presents this as his starting point, a state that was presumably transformed by Sai Baba. The very act of writing the book was based on Sai's command to 'dissolve his ego and surrender it at my feet,' implying a fundamental change from his initial cynical disposition. The inclusion of his past faults serves to highlight the transformative power of the Guru, suggesting that even a logic-driven and argumentative person can be changed.