A business unit manager was impressed by the competence of the internal auditor who was...

The principle most likely violated in this scenario is objectivity. According to the IIA Code of Ethics, internal auditors must maintain an unbiased and impartial mindset in all aspects of their engagements. By considering a job offer from a business unit manager involved in an audit, the auditor risks compromising her ability to remain objective both during and after the audit process. This situation creates a conflict of interest that can influence the auditor's judgments, potentially leading to bias in audit findings or decisions.

The Institute of Internal Auditors (IIA) - Code of Ethics