MINNEAPOLIS (WCCO) — Letgo is an app used by people who want to buy or sell used stuff — but Anoka County prosecutors say a man was beat up and robbed after using it to buy an iPhone 7.

(credit: Anoka Co. Sheriff’s Office)

Marcus Western, 19, and Johnathan Johnson, 18, are accused of robbing and assaulting the man in Columbia Heights on May 16. Investigators say they then tried to sell the phone on the same app.

(credit: Anoka Co. Sheriff’s Office/CBS)

Police found their ad, and then set up a meeting to buy the same phone. Western and Johnson were arrested when they showed up at the meeting spot.

Officials want to remind people to stay safe when buying or selling something through online advertising. Many law enforcement agencies have “Exchange Zone” areas set up in their buildings. The zones have surveillance cameras and emergency phones.