You have the ability to make inventory (some, or all) available only to your members and furthermore, only to those of a particular member type.
To do this, Add a new inventory item or Edit an existing item.
Select the MEMBERSHIP tab.
Set Member Only to Yes.
This will set the individual inventory item to be only available for existing members that have logged in.
If you wish to make your inventory item available only to those of a particular member type, there is one additional step.
Simply tick the box corresponding to the member types you wish the inventory to be available to online and click Save. This will mean that only those members that are logged in and have the selected member type/s will be able to view and select the inventory.
To reverse this and make an inventory item available to all. Simply select Member Only: No and Save.