Final answer:
The internal auditor should decline the offer of a free weekend use of the beachfront condo due to a conflict of interest.
Step-by-step explanation:
The internal auditor should decline the offer of a free weekend use of the beachfront condo from the manager of the marketing department. This situation presents a conflict of interest for the auditor since they are responsible for ensuring objectivity and impartiality in their work. Accepting such a gift could compromise their ability to perform their duties effectively and may raise questions about their independence and integrity.