I think the guy outside the store is just for the heart piece, but if you donate to him, the price for opening Malo Mart decreases significantly.

Edit: Wait, nevermind, you mean the guy in Castle Town, not the Gorons. *headdesk* All the talk about Malo Mart made me completely overlook your first post. That guy has nothing to do with Malo Mart. He'll give you a heart piece after 1000 rupees and never bother you again.