Removal of Illicitly Generated Items

I just want to know one thing. How do I know whether whether an item is duped or not? Literally half the items in the FM can be questioned whether it's duped or not. How am I supposed to upgrade my equips knowing that it could be deleted the next day for being illicit?

Obviously the solution is to hunt everything your own damn self, goldarnit!

Unless it vanishes anyway for no good reason like my old glasses. But you know.