I agree with a lot of the comments here. Grammar is not everything, but it is an important element in effectively communicating your message, especially if your target audience is native English speakers.
I have found that content advertised as written by a "native speaker" does not mean anything. Most Americans, Brits, Canadians and Aussies do not have good writing skills. I have bought a lot of articles that were supposedly written by native English speakers and have had to re-write almost every article that I purchased due to structural problems, grammatical errors and poor methods used to convey the concept.
I also suspect that most articles sold as written by native English speakers are just misrepresentations, especially when very few content sellers live in English speaking countries.
"Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote." -- Benjamin Franklin