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.

du boi was considered a radical because he wanted the immediate end for segregation. the biggest different between him and booker t. washington is that, even though washington believed that segregation should be considered illegal, he did not believe at all that a law was needed to keep blacks away from whites and that this would be something natural (to have the races apart) for a long time until society adjusted, while du boi believe that agitation was the only way to end segregation.