In August 2013, a couple met a man in the DoubleTree Hotel parking lot in South Portland to sell him a pair of diamond wedding rings appraised at $14,000 that they had advertised on Craigslist.

The man looked at the rings, pulled his shirt up to show them he had a gun, and left with the jewelry. When they tried to follow, he pulled the gun out and waved it menacingly.

The transaction would have had a different ending if the couple had met the man in front of the South Portland police station, under the department’s new Online Transaction Safety Zone.

In response to such incidents, South Portland police are encouraging people who go online to buy or sell items to strangers to consider doing business in the police station’s parking lot or lobby. The hope is that this will reduce the risk of being victimized by someone posing as a vendor or customer.

“The vast majority (of online marketplace patrons) have no ill will and are there to conduct a legitimate transaction like most of us,” South Portland Lt. Frank Clark said Thursday. “There are some who target these types of transactions to meet people and victimize them.”

South Portland’s police department is one of two in Maine and several across the country that have opened their lobbies or parking areas for people to meet and conduct business without fear. You don’t have to be a South Portland resident to take advantage of the department’s offer.

Augusta Police Chief Robert Gregoire said his department started encouraging people to conduct their online transactions there about three weeks ago, after reading an article about police departments in other states doing it.

“It’s very simple. It doesn’t really take up any of our resources and may actually save us some calls in the future,” he said. The police department in Hartford, Connecticut, has extended the offer, as have those in some smaller towns in Florida.

Craigslist officials did not respond to an email for comment, but safety recommendations on the website suggest meeting in a public place, bringing a friend, or making high-value transactions at police stations. Police say it’s also a good idea to get an alternative method of contact, such as a cellphone or email address, and write down vehicle license plate numbers when making a transaction.

Don Boucher of Rumford buys and sells everything from knives to backhoes and often uses online classifieds to solicit customers. He and his customers often meet in the parking lot of a business halfway between them because it’s easy to find. “Half the time I buy stuff I meet people somewhere,” he said.

While he’s never had a problem with a customer, he understands why some people might prefer the safety of a police station.

“I would say that for someone who’s timid, it’s ideal,” he said.

Meeting in a police parking lot offers a safe, well-lit area with the added benefit of video surveillance, South Portland’s Clark said.

“Not that we’re asking for a flea market to appear in our front parking lot, but if this tactic can help prevent someone from becoming the victim of a crime, that is, of course, one of the reasons that we’re here,” he said in a statement issued Thursday.

Risks exist for any person-to-person transaction, but Internet-based sites offer a level of anonymity that can attract unscrupulous operators.

“Based upon online posts, sellers and buyers, strangers to each other, need to arrange to meet in person,” the statement said. “Nationally, these meetings have resulted in criminal acts up to and including homicide.”

The most notorious case involving crimes in which victims were found through an online classified was the so-called “Craigslist killer.” Police say medical student Philip Markoff met women through Craigslist and then robbed them – in one case killing his victim. He was charged with first-degree murder and armed robbery before committing suicide in 2010 while in jail.

South Portland has had its own instances of criminals taking advantage of the online marketplace.

In one case in June 2012, someone offered an apartment for rent on Craigslist and collected the security deposit. Only later did the prospective renter realize the person did not own the property and had no right to rent it. In another incident in December that year, a cellphone sale went awry, leading to a fight and the arrest of four people.

In the case of the diamond ring heist, detectives were able to track the cellphone to the department store where it was purchased, gather video evidence from the store, link other leads to possible suspects and ultimately identify and charge Brice Charest, then 23, of Lebanon. Charest was convicted of robbery and sentenced to four years in prison.

Police said he also was a suspect in similar robberies in other New England states.