What was the motivation of the shopkeepers who denied oil to Sai Baba, and how did they react to the subsequent miracle?

Chapter 5 explains that because Sai Baba brought oil for free every day, the grocers eventually tired of it. They got a 'wicked idea' and conspired together, feeling that the 'nuisance must stop now.' However, after they refused him and then witnessed the lamps burning with water, they were amazed. The text notes they 'put their fingers in their mouths' in shock. They immediately felt repentance, realizing they had sinned by speaking an untruth and giving Baba needless trouble, and they began to tremble at his power.