Earlier quoted context omitted.
"You can order whatever you want unless a payment is made and product accepted a legal transaction hasn't occured." It may or may not be a crime depending on intent, but a transaction is not the issue. It is breach of contract. Laws obviously vary around the world, but the US Uniform Commercial Code is probably typical. The restaurant has made an offer. The customer has accepted it. There is agreed-to "consideration"…
Big orders require pre-payment. If no stock is available the customer should expect a wait. Even a pizza shop will require a credit card for 20 pizzas. If someone is selling 1 million dollars worth of widgets and the buyer is unknown prepayment is required. If known and a valid purchase order is signed the customer usually has net30/60 to pay if they don't there might be a lawsuit or a black mark on their credit file…
Whether you choose to avail yourself of such policies or not (including even getting the contract in writing) has no relevance to the legal question of whether a contract was breached.