MINNEAPOLIS (WCCO) — It has never been easier to buy and sell on the second-hand market.

Mobile apps allow people to shop and unload unwanted items from the convenience of a cellphone.

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But there is a risk. Two people were robbed last month while trying to make sales through an app. But a tech-savvy St. Paul police officer identified the thief.

“There’s a lot of apps out there and by and large they are safe,” said Steve Linders of the St. Paul Police Department.

Mobile market apps are an easy way to buy and sell items in seconds. The app Letgo touts convenience, using the phone’s GPS to highlight a potential sale nearby.

But two people learned the risk of accessibility last month.

“We don’t get a lot of reports of people becoming crime victims when they use [apps], but it does happen,” Linders said.

A woman selling her vehicle agreed to meet off Harrison Avenue in St. Paul. Instead of a sale, she was threatened and held at gunpoint while two men stole her vehicle.

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One day later, another victim hoping to buy an engagement ring through the same app agreed to meet off Western Avenue and Sturgis Street. He never got the ring, and instead was robbed of $500.

Police believe they have identified the culprit by using the app’s GPS technology against him. A Letgo-savvy St. Paul police officer posed as a shopper looking to buy a ring the app sent him to a potential seller at Youngman Avenue. When officers arrived, he took off.

As police search for the suspect, they have a reminder for consumers who are looking for convenience in the next sale.

“The app makes it easier and faster to find people to buy your items, but that doesn’t mean you can’t slow down the process and buy yourself a little bit of time,” Linders said.

Police do have some tips to avoid becoming a victim. They suggest people meet in a public place, like a police station parking lot. They also say use cash, research the person and check out their reviews.

Police do have leads on a second suspect. They have actually talked to two juveniles who were with the suspect and gave police information into the two robberies.

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There is no word on whether the two teens will face any charges.