Police in Bellevue, Wash., arrested a 17-year-old suspected of two armed robberies of victims targeted using the online marketplace OfferUp this past weekend.

The victims say they responded to OfferUp listings for a laptop and AirPods. The suspect allegedly confronted each victim with a handgun at the agreed-upon location and “demanded cash,” according to the Bellevue Police Department. OfferUp worked with Bellevue PD to identify the suspect within 36 hours of the first robbery.

OfferUp is an online marketplace, similar to Craigslist, with a more mobile-friendly interface. The company is based in Bellevue, just across Lake Washington from Seattle. Bellevue police say the incidents should “serve as a warning to anyone buying or selling items on an internet market site such as OfferUp or Craigslist.” They are urging buyers to meet sellers in public spaces and back out of any transaction that feels fishy.

It’s the latest in a series of OfferUp-related crimes that grab headlines across the country. But Bellevue Police and OfferUp say the vast majority of sales are safe.

OfferUp says criminal activity is “incredibly rare” on the platform. The company has doubled down on safety over the past few years. Buyers and sellers are encouraged to meet at monitored Community Meetup Spots, which are established in partnership with law enforcement agencies around the country.

“While the vast majority of these sales go off without a hitch, a few safety precautions will go a long way to preventing yourself from becoming a victim,” Bellevue PD said Monday in a blog post.

Earlier this year, OfferUp began rolling out a new service called “Hold Offers” that let buyers reserve items with an authorized payment before meeting up in person. The company said Hold Offers would protect sellers against “flaky buyers and sellers.”

Update: Offer Up has suspended the Hold Offers feature while the company works on improvements.

OfferUp is one of the top shopping apps in the iOS and Android stores. It has been downloaded more than 80 million times and 44 million people use the service. OfferUp has 260 employees in Bellevue and is hiring for about 15 positions at a new Miami outpost. The company is a rare Seattle area “unicorn,” valued at more than $1 billion.

Editor’s note: This story has been updated to note that Hold Offers is suspended.