there could be some kind of a mage ( like the merc healers ) that would unbound items in exchange of a good price, that way some item we'd like a lot wouldn't be lost but an high-price would be paid, so if someone would intend to unbound the item in order to sell it on the free market, their gains would be just slightly above what they would make selling it in the NPC shops.
please consider this, as I think many people don't invest a lot in excel items because they know they are loosing money as the item will be garbage some lvls in the future.
this would also make people invest more on mercs.