Since Sai Maharaj's goal was to teach detachment, is it true that he never accepted Dakshina from Kashiram?

This is incorrect. The account in Chapter 0 actually describes the opposite. While it mentions Maharaj did not take Dakshina in general at that time, it makes a specific exception for Kashiram, stating that 'he would always take a paisa or two from Kashiram.' In fact, to cure Kashiram's pride in being a giver, Maharaj later 'started a barrage of demanding Dakshina from him,' even instructing him to borrow money when his own ran out. This shows that Maharaj did accept Dakshina from Kashiram, and even used the act of taking it as a spiritual lesson.