Hilariously best by dates aren’t actually enforced by any agency or department so I don’t believe anyone is legally obligated to discard it. The dates are a best guess by manufacturers, the determination if something is actually spoiled is up to the end user.
But who determines if it’s expired? Obviously if they’re a resteraunt they have their own guidelines in order to adhere to the heath department, but what happens to goods with no best by date? The most I could see happening to an establishment is the being compelled to void the transaction or replace the item under some kind of anti scam ordinance.