in economics, this is called an 'arbitrage opportunity'
HMart (the Asian grocery store I tend to ridicule from time to time) sells Calpico, a Japanese soft drink, in two locations. One is in the main store and customers have to go through the checkout lanes. Those drinks cost $2.50.
About fifteen feet away is the start of the food court. If you choose to purchase a drink directly from one of those vendors, the cost for the exact same drink is $3.00.
I wonder if the sushi vendor buys Calpico wholesale from the main store.