Despite what you might think, it isn’t easy to spot a counterfeit check. Fraudsters know how to make a fake check look completely legitimate — so good that even a bank teller can’t spot it.

That’s why fraudsters are using fake checks to commit all sorts of scams, including phony prize awards, fake job offers, mystery shopper scams, and bogus online classified ad sales.

“This scam comes in many different variations” said John Breyault, who runs the National Consumers League’s Fraud.org website. “But the key thing that binds them all together is the use of a fake check. The consumer is instructed to deposit that check into their personal account and then send a portion of the proceeds to someone right away.”

A closeup of a checkbook. Michael Shake / Featureepics.com

Most victims are instructed to send the money via a wire transfer service, such as Western Union or MoneyGram. But some are told to buy prepaid debit cards or iTunes gift cards that they can use to buy things.

When the bank discovers the check is counterfeit — which could be days or weeks later — that deposit is removed from the victim’s checking account. The crooks already have their money and the poor consumer is left holding the bag.

Earlier this year, the Better Business Bureau released a list of the Top 10 Most Risky Scams based on an analysis of complaints collected through its online Scam Tracker. Fake check scams came in at number two, just behind home improvement scams. That ranking is based on how many people are targeted by the scam, how likely they are to fall for it and how much money the average victim loses.

The typical loss to a scam is about $275 — but with fake check scams, it's almost $1,500.

“This is definitely a very, very serious concern right now,” said Emma Fletcher, director of scam and fraud initiatives at the BBB Institute for Marketplace Trust. “The typical loss to a scam that’s reported to us is about $275, but with fake check scams the median loss is almost $1,500. That’s a lot of money.”

While anyone can fall for a fake check scam, the BBB’s analysis shows that men between the ages of 18 and 24 are the most susceptible. This is also the top scam for students, and military families and veterans.

These Crooks Are Clever

Fake checks are commonly used to steal money from people who want to become mystery shoppers. Kathy, who lives in Dallas, Texas, got taken for $2,650 this way. She asked that we not use her last name.

“What these crooks are doing is disgusting, absolutely disgusting,” Kathy told NBC News. “They’re really clever and they need to be brought to justice.”

Kathy had done mystery shopping before, so she wasn’t surprised to get an email from a mystery shopping company asking her to do some work for them.

“The email seemed totally legit and everything on the website seemed on the up and up, so I didn’t question it. There were no warning signs,” she said.

Kathy’s first assignment as a “survey agent” was to rate money transfer companies. The mystery shopper scammers sent her a check for $2,850 and emailed her a list of questions to fill out about her experiences.

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“It was a cashier’s check and it looked totally legit,” she said.

Kathy was told to deposit the check, take the cash and go to three different money transfer services and wire $900 from each. That left her with $100 for doing the job. She did as instructed.

About a week later, Kathy got a letter from her bank. It said the $2,850 check was counterfeit and couldn’t be cashed, so the money she had withdrawn would be debited from her checking account.

“The bank should have been able to determine immediately whether the check was legit or not and they didn’t. And that really disturbed me,” she said.

Kathy realizes she’ll never get that money back, but she hopes that by sharing her experience she can prevent others from becoming victims.

Why Fake Check Scams Work So Well

Few of us understand how the banking system works and the scammers use that confusion to trick us.

When we deposit a check, the financial institution is required by federal law to make the money available to us long before it can be certain the check is legitimate. We see the money show up in our account and assume the check is good and has cleared.

Fake check scam victims frequently report that their financial institutions decline to help them.

But that’s not what really happens. It may take a couple of days or a week or more for the check to work its way through the banking system and actually clear. During that time period, the bank gives us a short-term, no-interest loan using that check as collateral. If the check bounces, we have to pay back that loan in full.

“Unfortunately, you don’t realize you’ve been defrauded until you find that your bank account has a big negative balance,” said Fraud.org’s John Breyault. “And because of how our banking laws are written, it’s the consumer who’s on the hook for that — not the scammer and not the bank. It’s not like a fraudulent transaction on a credit card that you can dispute. It doesn’t work that way with personal checks.”

Victims Say the Bank Wouldn’t Help Them

People who’ve lost money to fake check fraudsters frequently complain that their bank teller did not warn them about the scam and their financial institution would not help them when the check turned out to be bogus.

Erika, a single mom in Oklahoma City who preferred not to be identified by her last name, was excited to be offered a work-at-home job this past spring. Her new employer sent her a check for $1,000 to buy office supplies and cover her first paycheck.

Erika was told to cash the check at her bank, take $979 to another bank in town and deposit it into the account of a corporate vendor who would ship the supplies she needed to get started.

A few days after she did that, Erika got a call from her bank. The check was a fake and there would be a $979 debit to her account. Not only that, but the debit caused her account to be overdrawn, which meant in addition to the $979 stolen by the scammers, she now owed the bank overdraft fees.

“I’m looking for a job, so I can provide for my three year old son, and instead I get fleeced,” she said.

Erika told NBC News she asked the bank if they could help her with this, but she was told there was nothing they could do. That’s not uncommon. Fake check scam victims frequently report that their financial institutions decline to help them.

The nation’s bankers insist they take fake check fraud very seriously and are doing a better job of spotting it and stopping it. For example, the American Bankers Association said tellers are trained to say something and ask questions when they see a transaction that appears to be suspicious.

“These losses are not something that bankers ever want to see,” said Doug Johnson, ABA’s senior vice president of payments and cyber security. “We continually educate our customers about the frauds being perpetrated against them, but we can’t stop every crime.”

That’s why it’s up to you to protect yourself and understand how scammers use fake checks to steal your money.

The BBB’s Emma Fletcher told NBC News she cannot think of any legitimate business transaction where someone would send you a check, ask you to deposit it and wire back the money.

“Any time you're asked to do something like that, an alarm should go off that this is a scam,” she said.

The Federal Trade Commission has information on Fake Check Scams and the Better Business Bureau provides 10 Steps to Avoid Scams.

Herb Weisbaum is The ConsumerMan. Follow him on Facebook and Twitter or visit The ConsumerMan website.