A group of Edmonton teens is giving a new definition to the phrase "steal of a deal" following a spate of violent robberies and carjackings that have occurred during online buy-and-sell meetups, police said Thursday.

Since Oct. 8, police have responded to nine incidents where a buyer and seller, using a secondhand marketplace app called letgo.com, arranged to meet to purchase — or sell — an item, the Edmonton Police Service said in a news release.

"We want to remind citizens to use caution when meeting up with strangers. Arrange to meet in a safe, visible and public location, not at your home or in your vehicle, and bring another person with you," said Det. Calvin Mah.

The suspects, who police describe as boys between the ages of 15 and 17 working in groups of two or three, have posed as both sellers and purchasers.

In some cases, said the news release, victims were threatened with a firearm or have been sprayed with pepper spray before being robbed of the electronics or vehicles they are trying to sell.

One incident, which took place around 1 p.m. on Dec. 3, a man selling a vehicle agreed to meet prospective buyers at his home in Baturyn. After being given the keys for a test drive, the two suspects stole the vehicle, dragging the seller for about 150 metres. He was uninjured, police said.

When posing as sellers, the suspects will arrange a meetup and then rob the potential buyers.

Letgo is a free app that has been downloaded more than 100 million times since it launched in 2015, according to the company's media information. The marketplace includes wares including electronics, cars and collectibles to housing, clothing and furniture.

Mah said people planning to attend a meetup should ask get a photo or description of who they are to be meeting with. If the person who shows up at the meeting point, doesn't match the photo or description, leave immediately.

"Above all, pay attention to your instincts," Mah said. "If something feels off at any point, abandon the sale."