When i sell stuff on eBay, i describe the un-opened items as MISB (Mint In Sealed Box). That way the buyers know that the figure is mint, as it has not been opened. I always thought MIB and MOC meant the same things, and describing un-opened items.

I never advertise items as MIB or MOC if they have been opened, as i always through my cards/packaging away anyway. If i sell an opened figure i'll describe it as "near perfect condition" or "used as display only".