At the end of mark twains narrative "i sell a dog" why does the narrator say that his principles remain intact

The first money that he earned for selling the dog was not earned because he sold a dog that did not belonged to him.  When he retrieved the dog and gave it back to the rightful owner, this time the money he received was rightfully earned because he corrected an error and had cleared his conscience in doing so.

the foundation of greek city-states: following the fall of the mycenaean civilization in the 10th century bc, the area surrounding the empire went through its own mini dark ages. answer and explanation