EDMONTON -- Buy-and-sell sites like Kijiji and Facebook Marketplace allow you to shop someone else's stuff. 

But Edmonton police are warning would-be buyers and sellers following a string of robberies involving cell phones for sale.

Police say last Thursday, a seller met with a man posing as an interested buyer in the parking lot near 144 Avenue and 75 Street.

But the buyer instead met the seller, pepper-sprayed him, grabbed the phone and ran.

About two hours later, police say a buyer met with a man pretending to be a seller near 128 Avenue and 44 Street to purchase a cell phone for $900.

When he arrived, it was reported he was attacked by two men armed with knives who demanded the $900 before fleeing.

Several days later on March 30, a near-robbery occurred in the area of Menisa Park, police said.

"In this instance, the suspect got into a vehicle with the seller and tried unsuccessfully to snatch the phone before producing a knife and fleeing on foot," police said in a news release.

It's unclear whether the three incidents are related, but police are questioning why anyone is meeting up during the COVID-19 pandemic.

“There’s no easy way to examine and test the item and complete the sale while observing the two-metre distancing that is being asked of us by our health officials," said Det. Calvin Mah with EPS Northeast Division.

"If you must have a meetup, please do so in a safe, public location, such as the new EPS Safe Exchange Zone at our Southwest Division station, and practice social distancing and hand hygiene as recommended by AHS.”

The safe zone is located at the EPS detachment on 1351 Windermere Way. Police also recommend telling a family member or friend when meeting in person to conduct a sale.

Health officials are also recommending that people avoid these transactions while the COVID-19 pandemic continues.

"These are extraordinary times and we must adjust the way we interact with one another," AHS spokesperson Kerry Williamson said in a statement to CTV News Edmonton. "Unless the product or service you require is essential to your health and wellbeing, we recommend that Albertans refrain from purchasing or selling items that require in-person transactions at this time."

The buy-and-sell sites have also shared advice: Marketplace is encouraging physical distancing and proper cleaning, while Kijiji is advising people against using its site right now.