Can you share a story that illustrates how Baba helps devotees overcome their doubts and strengthens their faith?

Certainly. Chapter 35 recounts the story of Boss Dharamsee, who visited Shirdi with a skeptical attitude. When Kaka offered grapes with seeds to Baba, and Baba began distributing them, Dharamsee was troubled. He disliked that variety and was concerned they were unwashed. He even mentally questioned Baba's status as a saint, wondering why Baba would force grapes he disliked upon him. Recognizing his inner turmoil, Baba commanded him to "Throw them in and eat." When Dharamsee obeyed, he was astonished to find the grapes were completely seedless. This powerful experience shattered his doubts and clinical scrutiny, replacing his ego with a profound love and faith for Sai.