Mel Kirkland was just trying to do a favor when she listed a friend's evening gown for sale on the online classifieds site last month. She didn't realize it might also make her a target of con artists.

Soon after posting the advertisement, the Summerville resident received inquiries from two people interested in sending certified checks to purchase the gown for $150.

Over the next several days, Kirkland received more e-mails from one buyer who went by the name Elizebeth Edwards. Edwards explained that her bank had mistakenly mailed a check for $2,150 to Kirkland. She asked Kirkland to deduct the amount of the gown, keep another $100 for her troubles and wire the remainder to an associate in Indiana.

Kirkland was immediately suspicious. She had read warnings on craigslist about scam artists trying to bilk people out of money by sending counterfeit checks for purchases. The scam works this way: The seller's bank cashes the authentic-looking check and the seller sends the extra money back to the buyer. Then, the bank discovers the check was bogus and deducts the full amount from the seller's account. The seller loses big money.

When the check finally arrived by Federal Express, Kirkland decided to investigate. She tried to call the Los Angeles accountant who supposedly approved the check, only to find no such person existed. She called the Connecticut bank that purportedly issued the check and learned it had changed its name four years before. The bank couldn't verify the check's authenticity and asked her to send it to their fraud department.

Edwards apparently lost interest as soon as Kirkland failed to cash the check and wire money. "I never heard from her again," said Kirkland, who still hasn't sold the gown.

Craig Butterworth, spokesman for the FBI's Internet Crime Complaint Center, said experiences like Kirkland's occur with alarming frequency. Internet auction and sales sites provide swindlers with a ready platform to do business, he said.

Butterworth advised buyers and sellers alike to learn as much as possible about the person they are doing business with, avoid requests to wire cash or accept personal checks, and always use secure payment options, such as credit cards or PayPal. "Doing your homework can really pay off, because if you can imagine it, the bad guys have already done it," he said.