You order an article from a writer. You receive your article. At first glance, it appears very well written. You submit it it Copyscape Premium, which confirms that the article is totally original.
Don't stop there! Copyscape is not enough! Copy (by hand; not cut & paste) one 10-word phrase (preferably across 2 sentences) between quotes into Google's search box.
I did exactly that, guided by my investigator's flair :-) and I found out that my "writer" actually copied 2 entire pages of a book. The book is available on Google books, and is searchable through Google, but NOT through Copyscape.