Why did Sai Baba refuse to take Dakshina from the wealthy Parsi merchant Ratanji?

The premise that Sai Baba refused Dakshina from Ratanji is incorrect according to the source material. In fact, Chapter 14 explicitly states the opposite. When Ratanji came for darshan and prostrated at Sai's feet, Baba immediately asked him, "What Dakshina (offering) will you give Me? Then you will be fulfilled." The text further elaborates that it was Sai Baba's common practice to ask for Dakshina from everyone who came for his darshan, regardless of their religion, be they Hindu, Muslim, or Parsi. He would even ask for large sums of money.