In the reading the shop keeper charged a fair price, and the same price to all customers. There were three possible motives good business practice, sympathy towards customers. Lastly doing the right thing because she felt it was right. Kant noted the last option as the highest motive.
I feel that the third motive of doing what was right could be a good example of acting out of a sense of duty. In my opinion acting out of duty is simply doing what’s right because you are obligated to. Now the shop keeper is only obligated to provide the product the price