Well, I wouldn't get discouraged. Your ungrateful buyer admitted there was only one article with abysmal quality, and if he's such a genius, why doesn't he write his own articles?
Besides, you have 1226 Reviews, only 3 of them are negative. As someone has said, "those who have never failed, have never tried." In fact, I wouldn't even call it a failure, this buyer didn't know you so why order 10 articles instead of one?
P.S. Data Analytics in Marketing? What is that? Customizing Google PPC? Selecting an audience on Facebook? That's a great topic for someone who graduated with a degree in marketing.
P.S.2. Sometimes it's OK to refund an order. I know Fiverr wants a 100% completion rate, but they're being completely unrealistic. Still, I am making more revisions than ever just to increase my rate.