You are right there are many hopeless teachers around too, but this does not mean that unqualified tutors are good. Good teaching is like health. If you are healthy, it means your heart, your brain, your liver you name it , all work well. If any of them does not function well then you are not healthy. To be a good teacher you need to be trained to be a teacher(a degree in education), you need to be passionate about teaching you need to have the ability to teach and also experience is the other element.