It's fair to say that Mr. Chong is not the world's best piano teacher. For one thing, he's deaf. For Suyuan Woo, however, he has a distinct advantage over the competition: he's cheap. In fact, his "expert" tuition doesn't cost her a dime; she simply offers to clean his house in lieu of payment.
Although this arrangement may work out just fine for the two adults, Jing-mei gets the worst of the deal because she's unable to progress as a pianist with such an unsuitable teacher. But Jing-mei never really wanted to play the piano in the first place; this was always her mother's idea. In any case, Suyuan Woo's choice of Mr. Chong turns out to be a false economy, which thwarts her long-held dream of Jing-mei's becoming a world-renowned prodigy.