According to Chapter 29, was receiving money from Sai Baba guaranteed? What principle governed his charity?

No, receiving money from Sai Baba was not guaranteed. Chapter 29 explicitly states that while his distribution of money was a true and regular occurrence, his manner was never fixed. He would not give to everyone who asked, and sometimes he would send people away empty-handed. The chapter explains this by stating that only those whose "auspicious time had arrived" would receive this blessing. The principle governing his charity was not based on the seeker's demand but on a form of divine grace, where the "touch of a saint's hand" was a fortune obtained only by the truly fortunate.