It is hard to decide who to trust as an English teacher, especially when you want to improve your writing skills. A moment's reflection is needed to realize that a native speaker of English does not always make a good one. Just consider how many Japanese native speakers know sufficiently about Japanese grammar to teach a foreigner how to compose a Japanese sentence properly. Therefore, we have to sort out native speakers who have enough knowledge and experience. That brings me to the second point. How can we do so? Although there are a lot of online services that correct your English composition, as far as I can see, it seems that they are employed by employers who are not sure how to distinguish a competent teacher from an incompetent one. There was a teacher who said that the two phrases "whether to do something" and "whether you will do something" have the same meaning. After all, it seems safe to me to choose a writer who is said to have been able to write a clear, profound and rhetorical English and imitate their sentences for the time being.