If he has bought armor and charged you a building fee, then possibly fair enough. If he is buying and selling for a profit, then probably not. Will be interesting to see what Tim has to say - he's a member here (same user name as that email address, so I assume the same guy @7w1n9m4n7)
So, who was the maker of the armor? If it is decent armor, then $725- you're still not that bad off. If it is rubbish armor, then that is the reason we tell people to stay away from ebay/facebook, etc. Look to the trusted sellers listed here.