There's no doubt that some copywriters will just scrape by... that's just the nature of humanity and freelance work. But by asking for samples before hiring and explaining the content you want, the writer can take your concepts and add copywriting techniques, emotion, and structure to it.
I recommend Upwork, because you don't pay for the content until you approve it (unless you do hourly work). As to your later comment about paying $40 per each article, I think that might be your problem. That's a pretty low rate, which is probably why that freelancer took a short cut. Not acceptable by any means, but understandable from an outside perspective.
As a rule of thumb, paying around 15 cents per word or over $30 per hour will more likely get you a quality freelancer. I'd also suggest going for 700-900 words per article. That'll help with SEO as well as just fleshing out your article. Shorter articles are OK sometimes, but the longer ones will gain more traction in the long run.
If that's just not in your budget, it's worthwhile to practice your writing skills. I'm working on an article this week for New Horizons on how non-writers can write using a simple formula that I personally use all the time – I hope that'll help in the future (if you see it), but also online research will probably yield some helpful tips, too.
