Great problem they're tackling. Some issues: Splitting inventory is an expensive activity. Often times you need to purchase more overall inventory and incur mo

Great problem they're tackling. Some issues: Splitting inventory is an expensive activity. Often times you need to purchase more overall inventory and incur more warehouse receiving cost when you try and divvy up your stock around the country to decrease average shipping times. They don't own their warehouses. This can be an issue if something goes wrong (eg they lose track of a large portion of inventory). Often warehouses hire temporary and low-trained workers. Things can go wrong if the warehouse doesn't have proper operational controls and can stay wrong for days (months even!) if a warehouse doesn't have a proper support team. Since they don't own the warehouses these issues are difficult to control for. There's some competition in the space like Shipwire owned by Ingram Micro (who also lease space to Amazon). Also I believe you can use Fulfillment By Amazon (FBA) to fulfill customer orders even if an item isn't listed on Amazon.