The Chronicle of Higher Education has a video tour of an essay mill. It is great. The funniest thing for me is the notice for essay authors after logging in (mark 3:20):
Please, stop using Turnitin Software!
Since Turnitin stores the papers in its databases, if a plagiarism-free paper is checked with Turnitin and then submitted again by the student, it will be now be flagged as a plagiarism, causing much dismay for the dishonest student.
What I find dismaying is that the essay authors are only paid so little for there work. The mills are making an enormous amount of money on this operation. I find ads that charge 30$ / page for an original paper, but the authors seem to only be offered 3-5$ a page.