The enable online selling checkbox is to put it live to the online store. If you want to put it to the online store without selling it, set the inventory to zero. This will disable the add to cart button for the product. If you want to describe how to order offline, you can add this to the product description.
In addition, you could remove the add to cart button from the code instead of setting the inventory to 0. This will allow you to show the products and not have the cart enabled.