This is possibly more of a discussion topic than a question, so perhaps out-of-place here. And you say 'professional' - but professional what? Professional teacher? To me, as a native speaker, a relatively regular participant here, and an occasion teacher of outdoor skills - I can tell you that there is a lot more to teaching than knowing your subject matter. I know how to write English relatively well, but I don't understand a lot of the grammar rules that describe how we actually write and speak. I have learnt more by trying to understand grammar questions here than I did in all my previous life. It is those rules that you need to be able to explain to a learner, to enable them to learn. It isn't enough to just say 'like this' or 'not like that' - you need to understand the reasons and know explanations. There is also a lot of psychology that goes into teaching. Knowing the ways that people learn, knowing how to teach effectively, and how to give feedback effectively are things that you need to learn, before you can be an effective speaker.

Well the benefits of a professional, is they are a professional. They have experience teaching people, know common issues people have, and how to work around them. A native speaker might probably could help you learn a language. But a professional teacher is going to know more ways to teach, and how to help any issues you have. So, if you can't afford. or just don't want to pay a teacher, you might be able to get away just by talking to natives. But you'll probably get more results, quicker, with a teacher.

Many native speakers 'picked up' the language without learning it. They know what is right but they often can't explain it. A non-native teacher has had to learn the language to a certain standard before becoming a teacher and can usually explain the reasons for grammar. There are some very good non-native speaker teachers and there are some very poor native speaker teachers! As Gary said there is more to being able to teach something than just being able to do it well. A good teacher will have a variety of teaching skills which have often been improved on with time and experience. Bob