Can you tell me the story about Sai Baba and the grapes that turned seedless?

Certainly. This incident involves a man named Boss Dharamsee who disliked grapes with seeds. When a devotee offered grapes to Baba, Baba began distributing them. Dharamsee was given some, but he was hesitant to eat them due to his preference and because they were unwashed. As Chapter 35 recounts, he was troubled, but Baba insisted, "Throw them in and eat." When Dharamsee obeyed and put the grapes in his mouth, he was astonished to find they were completely seedless, demonstrating Baba's ability to know a devotee's mind.