Can you recount the story of the grapes and Boss Dharamsee from the sacred texts?

Certainly. According to Chapter 35, a devotee named Kaka brought grapes with seeds as an offering to Sai Baba. Baba began distributing them to the crowd, which included a curious but doubtful man named Boss Dharamsee. Dharamsee disliked grapes with seeds and was also concerned they were unwashed, as per his doctor's advice. He thought to himself that if Baba were a true saint, he would know his dislike. In response to this thought, Baba gave him even more grapes. When Dharamsee finally obeyed Baba's command to eat them, he was astonished to find they were completely seedless. This experience transformed him, as he realized the strange and impossible power of saints.