What are the rules for performing Guru service through charitable donations or financial support according to the preface?

The preface of the Shri Sai Satcharita does not provide specific rules regarding Guru service through financial donations. The text focuses on other forms of devotion. According to Chapter 0, writing biographies is a significant form of Guru service. While writing about politicians or warriors is a worldly service, writing about saints yields spiritual fruit. The author describes the best and most certain service as writing the biography of one's Sadguru, followed by personal study, and performing recitations like Parayans and Saptahs with pure faith and selfless love. This form of service, using body and speech, is highlighted as not interfering with one's worldly duties.