Ninja'd, but I am posting anyway... I agree with GeoLib.
I don't think that is true. Trader's effect happens on "would gain" and gaining the Transmute occurs after you buy it. If you use Trader to gain a Silver instead, you still bought a Transmute, and you would not get the free buy again.
Edit, it also still isn't really an infinite combo even if you give it the straight up "When you buy this, +1 buy." because you've got to have $0P to buy it. By the time you Trader it away, or whatever you are doing... well, you already spent your Potion, so you would need to have played a second Potion this turn to keep buying them. I think that version of the card is just fine. If you want to put 16 potions in your deck so you can buy 16 Transmutes and Trader them with Goons in play, I would say good for you man, that is going to require one hell of an engine to go along with the 3 card combo (plus probably a 4th combo card in Watchtower to trash all those Silvers).