Final answer:
The appraiser would be most concerned with the principle of highest and best use when advising the apartment owner of the economic feasibility of constructing a swimming pool.
Step-by-step explanation:
The appraiser would be most concerned with the principle of highest and best use when advising the apartment owner of the economic feasibility of constructing a swimming pool. This principle states that an appraiser must consider the most advantageous use of a property that is physically possible, legally permissible, financially feasible, and maximally productive. By analyzing the potential income and cost factors associated with building and maintaining a swimming pool, the appraiser can determine whether it would be economically viable for the apartment owner.