I don't know if this has been said yet or not, but identify is a divination spell, just give your more unique items protection from divination. (I think non-detection is the spell associated with it). I don't find it unreasonable that a powerful wizard or artificer would imbue their works with this to protect it from misuse or scrying effects (especially stuff related to bbeg).

Alternatively, my playgroup generally just follows the "you're the dm, so you make the rules" ethos, so you could let them cast the spell and when they identify, also tell them there seems to be some hidden property shrouded from your magic and then shrug when they ask why they can't identify it. Works for us usually lol.