Chances are if you buy goods from Kijiji or Facebook Marketplace you will be fine. Most stories I know of have been positive. Still, you are taking a risk buying or selling goods to strangers. To reduce the risks, read this: Toronto police warn of thefts involving Kijiji and Facebook Marketplace sales.
I would not recommend large cash transactions either. If you are about to meet a thief who knows exactly how much you are bringing to your exchange point, that is a recipe for disaster.
Stay safe, shop well. Good luck!