Over ten years ago, I was a college lecturer and back then, checking a suspicious writing style was as simple as taking a long sentence and sticking it into a couple of search engines in quotes. Sadly, back then I would almost always catch someone passing off like half a research paper worth of stuff that wasn't theirs. In the last years before I left academia, the percent of students in each class I would catch plagiarizing grew noticeably over time. (more internet = more lazy) I can't imagine doing that job now... at least not with courses that require much writing... But if I had to do it again, I'd probably go with Copyscape. I used that one to check some work on a freelance project a few years ago and it saved my butt big time from some bad outsourced work... Great tool!