N. (suggestion) Allow not setting the inventory and have the system just behave as if it is always in stock. This is vital for anyone who sells on more than one marketplace, as the inventory will be wrong any time something sells somewhere else. Either that or the seller allocates a limited number of inventory to each marketplace and then one of them invariably sells out even though you're sitting on a pile of inventory (allocayed to the other marketplaces). Either way it's bad. More options are better.