The woman ahead of me at the bank looked grim.

Could the teller help figure out whether this check was good? The woman had received it as payment for a "mystery shopping" job, and she suspected it was a fake.

The teller didn't know either.

Last week, the Consumer Federation of America, a Washington, D.C.-based consortium of U.S. consumer groups, launched a task force to deal with fake checks and give consumers details about the warning signs.

Roughly one of every three adults has been approached by someone offering a fake check at one point, the group said.

About 2 percent of those are taken for amounts averaging between $3,000 and $4,000 each.

"Most people are honest and think that other people are too," said Susan Grant, the federation's director of consumer protection. "They get a very real-looking check or money order that comes with a plausible story and they don't understand that they will be held liable when it turns out to be fake."

But how can a deposit cost you money? The con artist asks the recipient of a fake check to pass on a portion of the proceeds to a third-party conspirator -- by writing a personal check off the victim's account or wiring money to another bank.

Jill Parker of Chicago, for example, said she and her husband were trying to rent out an apartment and placed an advertisement on the Internet.

They were contacted by a man in Britain who said his company was trying to open an office in Chicago. His company would make out a check to the Parkers for his moving expenses, he said. Could they take out their portion for the rent and pass the rest on to his agent?

Parker said both the executive and his request sounded legitimate, but the couple waited until they thought the check had cleared before they wired $22,000 of the $25,000 they'd received to the agent. Weeks later, the bank called them with the bad news: The check they'd received was bogus. Their account was being debited for the entire $25,000. They were out $22,000 and a renter.

Why did their bank clear the check in the first place? U.S. banking laws demand that banks give customers access to their funds within one to five working days. (The timing depends on whether the check-issuing bank is foreign or domestic, local or out of state.) But it can take several weeks for a good forgery to make it all the way back through the check-processing system to the point when your bank determines the check was fake.

It's worth mentioning that many of these fake checks look so real that they easily fool bank tellers, Grant said. They can be drawn on a real company and appear to be issued by a major bank at which that company has an account. That can make it particularly difficult and time-consuming to figure out that the check is a forgery. Nonetheless, when the bank determines that the check isn't valid, it's legally allowed to deduct the money from your account.

That's something that consumers commonly misunderstand, Grant said. The Consumer Federation conducted a recent survey and found that 59 percent of consumers inaccurately believe that when you deposit a check or money order, your bank has determined the funds are good before it allows you to withdraw the money.

The younger and less educated and affluent you are, the more likely you are to be misled.

This misperception affects 70 percent of 18- to 24-year-olds and 71 percent of those earning less than $25,000 and those who didn't complete high school, according to the survey. More than half of all the youths and Latinos surveyed also believed that if the check was bad, the person who provided it would have to reimburse the bank -- not the depositor.

Not true. You, the depositor, are responsible for the money that goes in and out of your account. If you deposit a fake check but don't draw against it, the worst that can happen is that the money temporarily credited to your account will evaporate. But if you use that phony balance, you're responsible for any check or money order you've sent, even if you've been swindled. Continued...