Final answer:
The external incentive related to a manager's interest in future career opportunities is reputation. Reputation is vital for both managers, affecting their future employment prospects, and for firms, impacting customer retention and investment potential.
Step-by-step explanation:
In order to maintain solid job performance, firm owners may rely on a manager's interest in working for another firm someday. The type of external incentive this represents is reputation. Managers know that performing well will contribute to a positive reputation, which in turn can open opportunities for career advancement in competitive markets. This incentive related to reputation is crucial since it impacts the manager's future employment potential and the likelihood of being hired by other profit-seeking employers who make decisions based on economic factors and productivity.
Building a strong reputation is also fundamental for firms themselves. It assures customers and investors of the quality and reliability of their products or services, often allowing such firms to charge higher prices or receive more capital investment. Therefore, a manager maintaining a high performance is aligning with the firm's overall goal of building a solid reputation in the competitive market.