The shoeshine boy is the odd one out because he is self-employed. He owns and operates his own small enterprise to earn his livelihood. The other three options - rickshaw puller who works under an owner, mason (a construction worker), and mechanic shop worker - all work under someone else. They are either casual wage labourers or regular salaried employees. As per the textbook, construction workers like masons are categorised as casual wage labourers, while those working under others (like the rickshaw puller under an owner or mechanic shop worker) are wage workers, not self-employed.