How do you tell if Permanent NX item really is Permanent?

4) If you purchase the nx item from a player, does it expire after some time (meaning you hold on to the item but don't equip the nx item) or "disappear" after equipping the nx item?
The expiration timer starts from the moment the item is unboxed in the cash shop, not when you purchase or equip it.

How about the ones that supposed to be permanent? Same deal? I was told in game that after buying from another player or in those free market stores the item sometimes "disappeared" after 24 hours or upon log off. :/

But thanks for responding. ^^

Stuff that expires shows the expiration date

That's true, but I am a bit skeptic of buying those so called "permanent nx items" from other maplers (not the ones in cash shop), also I am not a rich mapler.. :-(