With its free classified advertising in the online marketplace, Craigslist has established itself as a useful tool for anyone looking to buy and sell, job search or rent. Yet as with anything free, comes a burden of responsibility: Buyer beware. There's no way Craigslist can monitor the thousands of advertisements that post across the free site, although it posts a tip sheet to protect users from falling victim to con artists.

'A lot of times what happens is, products might be advertised as being for sale, but it's all a scam... They're just using a photo of a car and a price that may be too good to be true to lure you into taking the bait,' said Jenny Schearer, spokeswoman for the FBI.

In fact, with one long-running scam, if you list an item of worth, you can pretty much count on receiving an email with bad spelling and broken English offering to send you a check from overseas. They may send you a false check for too much money, and if you're extremely gullible, you happily refund the difference... (But now that you've read this, not anymore, right?)

'You have scammers patrolling Craigslist all day long,' said Robert Siciliano, security expert at McAfee, a computer and Internet security company. And some of the scams border on weird.

Here is a list of some of the more unusual scams.

The Baby Scam

Scammers posted an ad last year for 'a 2-month-old female for sale' on Craigslist, claiming the child was too much to handle. They were willing to sell her for an undisclosed amount. After receiving calls from concerned citizens, Fairfax police contacted Craigslist, tracked the advertisement to a home in Annandale, Va., and seized the computers. No baby was found.

The Adoption

An ABC special recently featured a successful adoption off of Craigslist, but that could lead to more adoption scams. One such con used a stolen photo of an infant from a mother’s blog and advertised 'a cute baby for adoption.' The catch? It would only cost $300 to start the adoption process. Luckily, a friend emailed the mom-blogger the photo and the mom reported the scam.

The Ticket Scam

You're scouring the web for tickets to a sold-out game, and there's one with a selling price of $200 to $400. The name of the seller is actually a reputable ticket seller. You order a ticket, give your credit card information (or wire money) and sure enough, an electronic ticket with a bar code appears in your inbox or mobile phone. The only problem is, when you show up at the game, you can't get in, because someone else has shown up before you using the same ticket, with the same bar code. In fact, that ticket may have been sold hundreds of times to unsuspecting fans.

In another ticket scam, you email for the tickets, the seller calls you and gets your credit card information, pretending they're from a legitimate ticket seller company. Your tickets never arrive.

One scamer used TicketCity's good, established name.

'The person is just trying to get the credit card information so they could sell it to somebody else,' said Randy Cohen, CEO of Austin-based TicketCity.

The Great Remote Service Provider

It's amazing what people will do to scam you. When I launched my freelance writing career, I needed a website built inexpensively to showcase work, and I listed the job on Craigslist. Many people responded with good portfolios, but a 'Canadian' guy named Richard was the most aggressive about getting the job. Sure enough, after I hired him, over the next month, he did a terrific job on the site; even building animated video into it, all for $100. When it came time for me to pay him, I was eager to do so.

I clicked on the Paypal invoice Richard had emailed to me, only to find it didn't allow me into my Paypal account. Richard had actually billed me with a fake Paypal invoice, and, as I went to log into the phony site, he was able to collect my Paypal passwords, which meant he could potentially use them for purchases and drain my credit card, and any bank accounts associated with my Paypal account. Luckily, I figured out the scheme in advance and changed my passwords quickly. 'Richard' tried to explain that he billed me with a false invoice because he was actually in Pakistan, and Paypal wasn't working for him properly. It is still amazing to me that Richard had spent a month on the scam and had even built me a website.

The Craigslist Romeo

'Anna' was a lonely woman looking for love on Craigslist. She put a photo of herself on the Web, and suddenly, a handsome man began writing to her. The two corresponded for weeks. He told her he was from the UK, that his wife had died in a car accident and he was looking for a serious relationship, marriage and children. Over the course of their emails, Anna's feelings grew. This was someone she could really talk to; really open up to. The only problem was that he was overseas. But as time passed, she felt she had to see him. He told her he admired her independence, and was willing to split the price of a plane ticket so they could finally see each other. Anna agreed. Romeo soon found a great deal on a plane ticket and asked her to wire him half the money. She did. Then he said he 'lost his job' and suddenly, he was asking her to wire the full price of the ticket. Once she did, her Romeo vanished, never to be heard from again.

'That scam is so unbelievably effective because people are emotional and lonely,' said Siciliano. 'Loneliness often trumps common sense.'

The Cute Pet

'There are all kinds of pet scams on Craigslist,' said Siciliano. It might be an adorable lapdog that belongs to a college student whose roommate is allergic to it. The dog is being sold at a discount, with pedigree papers, and could be headed to a shelter if you don’t help out. If you send them the money, they'll promise to put the dog on a flight to your airport. You might even be given the opportunity to pay half up front, and half later, said Siciliano.

Of course, the dog doesn't exist.

The Perfect Apartment Rental

In another case, Siciliano actually fell victim to a scam. A day after he listed an apartment in Boston for rent, he found people trying to look at it from his driveway.

The scammer who went by the name 'John Sawyer' had stolen his photos and reposted almost the same advertisement with his address, for half the price, and with different contact information.

'The scheme was the landlord was out of town,' said Siciliano. But the people were told they could pass by the street address if they chose, and then send a deposit for first and last month's security.

'People just showed up at my house,' he said. If they hadn't he may have found someone on his doorstep with their suitcases, ready to move in after paying the scammer.

Since he works in web security, he knew to contact Craigslist Abuse and flag the ads for removal.

'But (the scammers) kept posting similar ads,' said Siciliano. 'I pulled down like half a dozen ads.'

The Investing Answer: Dealings on Craigslist are like posting a sign on your lawn. Never provide banking or social security information. Try to deal locally with people you can meet in person. Never wire money, and remember that anyone who asks you to do so is probably a scammer. Fake cashier checks and fake money orders are common; banks will cash them and then hold you responsible when the fake is discovered weeks later. Craigslist never offers protection for purchases. Victims can file complaints with the FBI's internet crime complaint center, 'But, the reality is, if you lose several hundred or several thousand dollars on an online transaction, it's unfortunate, it happens a lot, but most likely you're not going to be able to get that money back,' said Schearer.