I read about an incident where Sai Baba seemed to show partiality by accepting money from one man but not another. Can you explain what happened?

The incident you're referring to is narrated in Chapter 36 of the Shri Sai Satcharitra. Two gentlemen from Goa visited Sai Baba for his darshan. Baba specifically asked one of them for fifteen rupees in Dakshina, which the man gave with joy. However, when the second man tried to offer thirty-five rupees on his own, Baba immediately rejected it. The text acknowledges how strange this seemed, stating that "Everyone was greatly surprised by this." This apparent partiality was so noticeable that his close devotee, Madhavrao (Shama), felt compelled to question Baba about his actions.