Is it ok for script author to do this on gmodstore?

Closing this out, Nook pretty much stated everything that needed to be said. Developers are allowed to deny you the ability to purchase their items. As long as it's not done in a way that is malicious or spiteful (IE: telling you to buy it, and then taking it back after they've got your money without just cause). We (gmodstore) don't police who they can and cannot sell to.