Why did Maharaj's approach to accepting Dakshina from Kashiram change so drastically, and what spiritual lesson was being taught?

Maharaj's handling of Dakshina with Kashiram was a deliberate Leela to address an obstacle on Kashiram's spiritual path: pride. Initially, Kashiram was so eager for Maharaj to accept his offering that he would feel dejected if it wasn't taken, which fostered a sense of pride in his ability to give. As Chapter 0 explains, it is God's resolve to remove such obstacles for a devotee. To counter this, Maharaj first refused Dakshina, then began demanding it relentlessly, even forcing Kashiram into debt. This difficult period was designed to make Kashiram realize that he did not truly possess the power to give. Once this lesson was learned and his pride was removed, his financial situation improved.