A private investigator is approached by a potential client who wants them to conduct surveillance on a former business partner purely out of spite, with no legitimate investigative purpose. What is the ethical course of action?

1. Decline the engagement, as it lacks a legitimate purpose and could constitute harassment.
2. Accept the case but only conduct minimal, discreet surveillance to avoid issues.
3. Advise the client to obtain a court order first, then accept the case.
4. Accept the case if the client pays a high fee, as long as no laws are technically broken during surveillance.