Users can order inactive catalog items.
The catalog item will be visible only if the logged in user has a 'catalog_admin' role.
For any user without the catalog_admin role, it will display the 'You are either not authorized or the cart item is invalid' error message.
In the example, We are taking 'Apple iPad 3' Catalog item.
As 'Beth Anglin' User is having 'catalog_admin' role, she is able to order catalog item.
As 'Abraham Lincoln' User is not having 'catalog_admin' role, he is getting 'You are either not authorized or the cart item is invalid' error message.
The user who is having the 'catalog_admin' role can test and work on any inactive catalog item as well. This is an Expected behaviour by design.