Is there some way to block items from being ordered if they are out of stock?
Response:
If you set the Depletion Status to "Sold Out" or "Discontinued" (within Settings/Site Options/Inventory Control), the customer is blocked from ordering the excess quantity, and the cart is amended as appropriate.
For any other Depletion Status however, the customer is notified of the situation, but is permitted to proceed with the order.