Then I could gain more hagglers with the haggler gain ability, while my opponent was locked out forever!
That is a cute opening, but it doesn't lock the opponent out of Haggler. He only needs to buy one Haggler and be in the same boat as you, only one Curse richer.
Now, if you can stack several Embargos on it before he can buy it, then that would be fairly meaningful, especially since you can use your Haggler to gain more Embargos, but a lack of +Action would likely obstruct this route.
Risking only one Curse doesn't strike me as a particularly daunting tactic. Swindler can put more Curses in his deck and without requiring purchasing it several times.
Although, any 5/2 opening can be improved with just because of its +$2.