Oho, nice! I didn't think of your versions of the Haggler trick. What I was thinking of was Haggler in play, buy the last Silver, haggle a Copper or something, reveal Trader, gain the last Silver instead—but that's a little inelegant because it uses Trader, which was already one of the other answers (though it uses it for something different).
One more! (Well, one more that I thought of before posting this puzzle.)