Can a slave permitted to trade also rent himself out or act as an agent for others?

Primary text

If a slave is permitted to trade, it is not permissible for him to rent out his services (yujir nafsahu) or act as an agent for another person. This is because such actions constitute a contract regarding his own person, which cannot be done merely by permission to trade, similar to selling or marrying himself. The slave acts on behalf of his master, not purely for himself, which distinguishes him from a conditionally manumitted slave (mukatab) who acts for himself and thus can sell to his master.