I have mixed feelings about this. I’d agree that most places that offer yoga aren’t all that great — just today I saw a photo of a local (NYC) yoga class and the teacher was teaching the posture (standing bow) all wrong and everyone in the class had seriously messed up alignment. And some of the corporate chains have been known to push people into teacher trainings. But there’s nothing like having a great teacher guiding you through things. I personally can’t imagine being where I am in my practice without all the teachers I’ve been lucky to have.