I think you have done an excellent job with your website.   I found it very easy to understand and navigate.   You break down the categories well.
The only thing I saw that I didn't like was when I tried to preview an article.   It was hard to read and the window scrolled way too quickly.   That made it hard for me to read.   And therefore I couldn't tell how good the author's English was.    And if I can't tell how well the author writes in English, then I certainly would never buy an article.
So, if I was you I would fix that.  Make it easier to see a preview of the article.   Make it really easy to read the preview.    Other than that, I think you have done an excellent job.