With the state licensing board for that profession in the state where the person practiced; some professions also offer national lookup tools.
No. Licenses lapse for many ordinary reasons, such as retirement, relocation or not renewing.
Often not. Many boards publish only final disciplinary actions, while dismissed complaints usually remain confidential.
Verify their license with the state board before sharing information or paying, and report anyone practicing without a required license.
Usually it shows current status. Request historical records from the board if you need status on an earlier date.