The mistake made by many in using this technique is in thinking that it is about selling carpet cleaning on the door step, it is not, or at least it shouldn’t be. People hate cold callers and do everything to get rid of the salesman that just turned up on their doorstep. So don't be a salesman. Why not just knock on a door and introduce yourself as their local carpet cleaner and ask if you can leave them with a business card or flyer for when they might need you in the future? When they take the card you simply thank the person and turn to walk away and you'll find that some people will say, 'well, while you're here we were thinking of having x cleaned,'
If you're pushy they will do everything to get rid of you and throw your card in the bin where you've gone.
Simon