Determining if someone wrongly influenced someone to write or modify a will is a factually intensive question.

Undue influence can invalidate a will in California. State law provides that a will or will modification is invalid because of undue influence if the will was made by a person under "excessive persuasion" by another person that overcame the will maker's "free will," resulting in "inequity."

How might undue influence look?

Examples that could create suspicion of undue influence:

An elderly person unexpectedly leaves everything to a health aide, disinheriting her beloved children.
A person with no close family has always said he would leave his estate to a particular charity surprisingly leaves a large amount of money to a neighbor who helped the person with errands and chores.
A widower unexpectedly marries a much younger second wife and redoes his will, leaving everything to the new wife to the detriment of his children, including a child with disabilities.

A common element in these examples is unfairness or inequity - someone who seems entitled to a benefit of the will because of a relationship, an expectation or a need will not be the recipient of that benefit.

But inequity alone is not enough to show undue influence. A person can legally choose not to leave money or property to an expected heir or recipient so long as the will maker was not unduly influenced by another person in making that choice (unless the will is invalid for another reason).

To put it in the words of state law, there must be "more" than just an "inequitable result" for undue influence to exist.

What is the definition of undue influence?

In 2014, two California statutes took effect that provides a modern, detailed definition of undue influence in the probate context, including in will contests. The definition had not been updated for more than 100 years. The new definition is supposed to "supplement" the "common law" meaning of undue influence expressed by state court judges in their opinions.

The law says that undue influence is "excessive persuasion that causes another person to act or refrain from acting by overcoming that person's free will and results in inequity." A court must consider:

Victim's vulnerability: For example, was he or she sick, disabled, elderly, illiterate, intellectually impaired, incapacitated, injured, in "emotional distress," isolated or dependent? Did the influencing party know of this vulnerability or should he or she have known?
Apparent authority of the influencing party: For example, was he or she acting in a professional or personal capacity of service to the victim such as a relative, medical or home care aide, fiduciary (like a guardian, conservator or trustee), medical or legal professional, "spiritual adviser, expert" or another person with specific qualifications.
Influencing party's "actions or tactics": For example, did the influencer misuse "affection, intimidation, or coercion"; control access to other people or to information; withhold sleep or medication; or control other "necessaries of life"? Did the influencer initiate "changes in personal or property rights," especially when the influencer claims to be an expert or uses haste, secrecy, or "inappropriate times and places"?
Result's equity: For example, had the victim expressed different prior intentions? Was the change in the will inappropriate considering the "length and nature of the relationship" or the economic disadvantage to the victim? Was the relationship with the influencer disproportionate to the value of anything given or left to the influencer?

The lawyers at Klein DeNatale Goldner with offices in Bakersfield, San Diego, and Fresno represent clients throughout the San Joaquin Valley in probate litigation, including will contests.