Vancouver police have issued a public warning after a string of robberies involving Facebook Marketplace users, including one terrifying incident that saw a seller robbed at gunpoint.

Authorities said that robbery took place Monday night inside a coffee shop in the citys Kerrisdale neighbourhood, where a Facebook Marketplace user arranged a meeting to sell a designer watch.

A suspect described as a man in his 30s with a beard walked into the coffee shop, pointed a firearm and took the watch before fleeing into a waiting vehicle, according to police.

Authorities said three robberies involving Facebook Marketplace users have been reported since Saturday, though its unclear if they are connected.

The victims in these recent cases seem to have done everything right – theyre meeting with someone they didnt know but they arranged to meet in a public location, Sgt. Steve Addison said. They still fell victim, and thats incredibly concerning for us.

On Saturday evening, a 21-year-old man was trying to sell a used phone through Facebook Marketplace and arranged to meet in Champlain Heights. Authorities said when the seller arrived, he was met by two men who appeared to be in their late teens.

They robbed him of his phone and hit the victim in the head with a weapon, then attacked him with bear spray, the Vancouver Police Department said in a news release. The victim was injured and required medical treatment.

Another Facebook Marketplace seller – a man in his 30s – arranged to meet someone in the same neighbourhood to sell two used iPhones around noon on Sunday. A suspect described as a teenage boy grabbed the phones and ran away, police said.

Investigators are still working to determine whether any of the Facebook accounts that were used to trick and ambush sellers were legitimate, but Addison said at least one account has disappeared since the robbery.

Police believe there are likely more victims of similar robberies – whether they involved Facebook Marketplace or a similar service such as Craigslist or Kijiji – and urged anyone who hasnt yet come forward to do so.

While investigators work to determine whether the three recent incidents are related, authorities noted that online buyers and sellers can meet at the police headquarters at 2120 Cambie Street to complete their transactions.

Its a safe location for people to do their business, and we want people to know its here and theyre more than welcome to use it, Addison said, adding that there are surveillance cameras as well.