People with dementia are at high risk because judgement and memory are affected. Warning signs include unusual withdrawals, a new friend managing money, unpaid bills despite sufficient funds, and sudden changes to a will or deed.
Adult Protective Services in each state investigates, and banks have reporting duties.
Why it matters
It is common, it is usually a family member, and catching it early is the only real remedy.
Sources
Where to check this, and where to read more. All external and all authoritative.