This shopkeeper is the person with the violet fate that he sensed earlier. He is thinking about how to do a great deed for them, and by the looks of things, his goal might be easy to achieve.
He made up his mind just as the shopkeeper rushed over to attend to him. He had entered the shop for a few seconds, so he hadn't been stood up for long. Even so, the shopkeeper apologized profusely to him.
The man bowed and said, "Please forgive me for not attending to you, senior. Please, how can I be of help to you? Ask me anything you want, and I will try to help you."
His humble behavior toward Arthur can be easily explained as due respect being offered to someone much stronger than him. Arthur could hide his cultivation so his rank and power were evident to anyone who so much as glanced at him.
