We could apply taxes if character is looming second set of armor, weapons, leg armor etc. For example, if you have already retired with, say, leather armor once, you will have to pay additional money to heirloom some other armor (gothic plate) - 100k for +1, 200k for +2 and 300k for +3.
Though it shouldn't be neccesarily taxes. Players may need some kind of tweaks and small-time bonuses for monetary charges.