It happened to Craigslist.

It happens to pretty much any new peer-to-peer classified marketplace.

And now Facebook is incurring the wrath of the media, which is reporting on a string of robberies between people concluding in-person transactions initiated on Facebook’s new Marketplace app.

In Little Rock, Arkansas, a man pulled a gun on a another man selling an iPhone; the two had met on Marketplace. While police in Little Rock advise exchanging goods only in a public place (they even offer up the local police station), in this case, the robber offered the seller more money if he’d come to his house, saying “his parents wouldn’t let him drive.”

In New York, a 17-year-old high school student agreed to meet a female buyer at a Tribeca skate park. Three other people, one wearing a ski mask, were waiting, and the seller was stabbed before the robbers escaped with the goods.

An iPhone sale was also at the center of an armed robbery in Des Moines, Iowa. The robber was savvy enough to block the woman on Facebook by the time she went to look him up to show police, but the woman’s husband found his profile anyway and took a screenshot of his picture, the Des Moines Register reported.

The Des Moines robbery calls attention to both the danger and potential advantage of using Facebook Marketplace over more anonymous services like Craigslist. Facebook users are, at least in theory, supposed to use their own names online, although profile pictures can be whatever the user wants.

Still, a Marketplace “best practice” might be for both sides to copy any identifying information before the sale – in case things go wrong.

Unfortunately, these negative incidents were to be expected. Nor will they be the last.

It’s not limited to just face-to-face nastiness, either.

Just a day after Facebook Marketplace launched, the online news site Quartz reported that the app had been “bombarded with illegal listings, for sex, guns, marijuana, baby hedgehogs, and more.”

Facebook’s director of product management, Mary Ku, told Quartz it was a technical issue that had prevented Facebook’s automated reviewing mechanism from flagging posts.

“We are working to fix the problem and will be closely monitoring our systems to ensure we are properly identifying and removing violations before giving more people access to Marketplace,” Ku explained. “We apologize for this issue.”

More recently, Action Fraud – the U.K.’s national reporting center for fraud and cybercrime – has received reports from victims who have tried to purchase items and never received them. Auction Fraud described one scam where fraudsters offer an item for sale and demand that payment be made via bank transfer. (Facebook Marketplace doesn’t have an online transaction tool of its own.) If a buyer asks to meet the seller in person, he or she is given an excuse with the suggestion that the item be posted by mail or delivery service after the money is sent.

The item is never delivered, of course, and the seller quickly blocks any messages come from the defrauded buyer. Action Fraud’s advice: never transfer money into a sellers’ account without viewing the item in person first.

None of this is meant to suggest that users should avoid Facebook Marketplace or that it has a problem any more serious than other classified ad services. But buyers should beware on Marketplace just as they would anywhere else.

Just because it has Facebook’s name on it doesn’t mean a the shady sellers out there will suddenly change their spots.