Criminals are using popular online marketplaces to set up robberies and Hartford police have issued a warning to keep users safe.

Hartford police said a person was robbed after attempting an exchange Wednesday night near Asylum Avenue. Officers arrested a suspect, identified as Daniel Marciano, who was armed with a BB gun, after he attempted another robbery where detectives from the Major Crimes Division posed as the potential buyer. Marciano is suspected in other area incidents.

Police also arrested three other suspects charged with conspiracy to commit robbery.

This is just the latest example of an ongoing criminal practice. Last year, Hartford police made over a dozen arrest in collaboration with federal officials after a series of online marketplaces exchanges turned violent, some escalating to the point of gunshots.

Police said a simple way to protect yourself is to meet at a police station. In Hartford, they’ve designated a point to meet up where video cameras will capture an exchange for an extra layer of security.

“Ever city resident, everyone from the whole state rather, come to the Hartford Police Department, come to any police department. They’re safe, transaction sites that are set up specifically to avoid this kind of confrontation,” said Lt. Pail Cicero.

Mall parking lots or meetings during the day may seem safe, but police said if a person says no to meeting at the police station, it’s a sign to end the conversation.