Can you recount the story of Appasaheb and the Fakir concerning the exchange of Rupees?

Certainly. As detailed in Chapter 33, Appasaheb, accompanied by two friends, encountered a Fakir who resembled a picture of Sai he had. The Fakir began asking for Dakshina. Appasaheb gave him a Rupee, then another, and a third. He then collected Rupees from his friends, giving the Fakir a total of six. The Fakir persisted, so Appasaheb promised more at his home. There, he gave three more Rupees, making it nine. When the Fakir still asked for more, Appasaheb explained he only had a ten-Rupee note left. The Fakir then took the note, returned the nine Rupees he had collected, and quickly departed. This story illustrates Sai's principle of ensuring a devotee's spoken promise is completely fulfilled.