Police are warning residents of a "mystery shopper" scam that has bilked millions of dollars from people nationwide.

Susan Whitehead, of Fairfield, says she received an email a few weeks ago inviting her to be a mystery shopper, supposedly to rate the shopping experience at some major retailers. Whitehead says she got a check in the mail for more than $1,500, which she deposited and then did some shopping.

Whitehead was then asked to refund what was left over to the company and mailed them a check for $1,380. She says that after she mailed the check, she was shocked to learn the original one was fake. She was left liable for the $1,380. Whitehead says she lives on a fixed income and is now unable to pay her rent for the coming month.

Police say that while legitimate mystery shopper programs exist, a real one will never ask for a refund out of your checking account. Police also advise waiting three weeks before spending any money deposited using a check.