Cal. CIV § 1575

Undue influence consists: 1. In the use, by one in whom a confidence is reposed by another, or who holds a real or apparent authority over him, of such confidence or authority for the purpose of obtaining an unfair advantage over him; 2. In taking an unfair advantage of another’s weakness of mind; or, 3. In taking a grossly oppressive and unfair advantage of another’s necessities or distress.