Once he retires, his duty changes. After retirement, he might get involved in doing business. Then he says that pursuing his business is his duty. Even though he may have now taken to lying and cheating in order to earn money, he will still consider the work he is doing as his occupation and his duty. These changing activities that occupy your time in the interest of providing for your living needs, cannot automatically be described as dharma .
Duty becomes dharma when it shines with the virtues that make up the facets of dharma .