Can you tell me the story of Kaka Mahajani's skeptical friend who visited Shirdi?

Certainly. Chapter 35 recounts the story of a friend of Kaka Mahajani who was averse to idol worship and only agreed to visit Shirdi out of 'clinical curiosity.' He made two firm conditions with Kaka: he would not bow his head to the saint, nor would he offer any Dakshina. However, upon arriving at the mosque, Sai Baba greeted him from a distance by asking, 'Why have you come in this manner?' As Chapter 35 details, the tone of Baba's voice was a perfect imitation of the friend's deceased father. This profound experience caused the friend to completely forget his resolve, and he immediately bowed his head at Baba's feet.