The majority of so-called cheat sites are American in origin. US schools are much more likely to use standard tests so the scope for the production and distribution of standard answers is that much greater.
For GCSEA-level students it's hard to see what a student might gain by either using an "off-the- peg" essay (presupposing they could find one that exactly answered a question they've been set) or by buying one written to their specifications. Depending on the site, a student could typically be asked to pay Pounds 6-Pounds 18 per page, a cost that is probably well outside the range of most students.
A coursework project "ready written" might be attractive to some students in the UK because this work actually counts towards their final exam grade. However, it is relatively simple for teachers to control for the possibility of cheating by taking the same precautions they take to guard against plagiarism (for example, asking students to discuss their work-in-progress, explain their thinking and so forth).
The quality of "off-the-peg" work offered by these sites ranges from the poor to the pathetic. Capable students don't need to get essays from such sites, therefore they don't submit examples of their work (something that is often a precondition for downloading an essay).
Cheat sites have little or no quality control. Rather than see cheat sites as some sort of threat, I encourage my students to visit such sites and download relevant materials to use as a source of ideas, research material, cross-cultural comparisons and so forth.
Chris Livesey 104 Tarn Drive Creekmoor Poole Dorset