Can you tell me the story of Boss Dharamsee and how Sai Baba transformed his skepticism using grapes?

Certainly. The story, detailed in Chapter 35, recounts the visit of Boss Dharamsee to Shirdi. Arriving with a "clinical scrutiny," he was curious about the miracles he had heard about. When Kaka offered grapes with seeds to Baba, Baba began distributing them. Dharamsee disliked this variety and was hesitant to eat them, even questioning in his mind why a true saint would force something upon him that he disliked. As this thought arose, Baba gave him even more grapes. When Baba commanded him to eat, Dharamsee obeyed and was astonished to find the grapes were now completely seedless. This direct, personal miracle shattered his ego and skepticism, replacing it with profound love and a firm resolve to return to Shirdi.