What it is
An overpayment scam pays you more than you were owed, then asks you to send the extra back. The first payment is fake or reversible, so the money you refund is your own and is gone when the original is undone.
How it reaches you
In a job, it arrives as a first paycheck that is too large, or a check to cover equipment, with instructions to forward the difference to a vendor or a coworker. See a job sent me a check to deposit.
The tell
A real employer pays you the correct amount and never asks you to return part of a payment. Being overpaid and asked to send money back is the scam.
What to do
Do not send anyone money, and tell your bank the payment is part of a scam. Keep the check or transfer details and report it to the FTC. It is a form of the fake-check scam.