Sorry, my mistake.
Phew, I thought he was seriously contemplating running a demo on how to remove draft marks!
This does though bring out the need for someone to run a Practical Carpet Cleaning Course because reading between the lines lots of people could really benefit from one. Although most courses cover the theoretical elements of carpet cleaning they rarely teach you HOW to clean carpets and hence the question that started this topic. For as much as you are only as good as you know your basics, you are also only as good as you apply those basics.
Draft mark removal, stain removal, wand technique etc etc are all learned skills that are clearly not being taught on today's courses, or is it the case that people are STILL coming into this business without so much as a minutes training! Surely not!