You receive a letter saying you've been selected to become a "mystery shopper" at an amazing $125 an hour! Enclosed is a $3,150 cashier's check and instructions to visit a local Wal-Mart customer-service desk and pose as someone buying a MoneyGram to wire $2,825 to a relative in Canada. The check amount covers the cost of the MoneyGram, including Wal-Mart's fee, and $250 for you for two hours of work, which includes filling out a survey on the service you received. It sounds like the quickest $250 you'll ever make.

But after you complete the assignment, you'll soon realize you've been had. Within weeks the financial institution where you deposited the check will notify you that it is fraudulent and that you must pay back the $3,150. What makes this scam particularly disturbing is how legitimate it appears. The documents are businesslike, and the cashier's check carries the name and address of an actual financial institution. The toll-free number, however, belongs to the scam artists. If would-be shoppers call it to verify the deal, they'll receive assurance of the check's "authenticity."

You might get such a letter after you post a résumé on a job site such as www.monster.com or respond to an online work-at-home promotion. The Federal Trade Commission has issued a warning about this and other check scams at www.ftc.gov/bcp/edu/pubs/consumer/credit/cre40.htm.