“In Canadian law, store employees or staff are not allowed to physically stop you from leaving or search your belongings unless they actually witness you commit an offence,” she said. “You are free to walk past a receipt check, out the store.”
She said the exception is when shoppers exit a retailer such as Costco, which can enforce receipt checks because people agree to them when they sign up for the required store membership.
Source
Edit: Unless you mean source for everything is a potato. That statement is self evident.
The potato thing was really just more about life in general. But it is useful for some specific applications.