It was gold in fact, that helped our hero. And Medea was smitten. Out of love, as women are wont to do to this very day, she helped Jase get his booty. Nothing much folks. Which, poor soul that he was, he promised on the spot.
Gold has a funny effect on people at times.
Eternal Marriage, my friends. A lifetime was not enough for her. Not to say that I wouldn't accept a deal like that if my wife offered it to me. And then a promise was another story entirely. Once he got his fleece he hightailed it out of there with his loot, and left Medea and her father in the lurch.