Undue influence (UI) is a psychological process by which a person's free will and judgement is supplanted by that of another. It is a legal term and the strict definition varies by jurisdiction. Generally speaking, it is a means by which a person gains control over their victims' decision making through manipulation tactics and unfair pressure, typically for financial gain. Historically, UI has been poorly understood, even in some legal circles.
Undue influence is typically perpetrated by a person who is trusted by the victim and is dependent on them for emotional and physical needs. Caregivers are often found to have unduly influenced their patients, however, anyone in a position of trust and authority over the victim (e.g. fiduciary) may be guilty. This includes the victims' attorney, accountant, nursing home attendant, or even children. UI is a process, not a single event. A manipulator may spend weeks, months, or even years before successfully unduly-influencing their victim. Anyone is susceptible to UI, but the elderly are particularly vulnerable. Perpetrators of UI operate in shadow, enacting their manipulation behind closed doors where there are no witnesses. A person being unduly influenced may become withdrawn, depressive and passive. Physical signs of abuse may include unexplained bruising, scratches, and/or broken bones. Other signs may include missing or broken dentures, prescription eyeglasses, hearing aids or other assistive devices.