[This really only works on super-religious types who find nakedness to be against their religion]
There was a knock at the door. I answered it wearing two rather fetching hot pink towels (one on the head, one on the body). There stood two very smartly dressed men who I soon realised were Jehovah’s Witnesses. They took on elook at me, threw a pamphlet in my direction and ran away.
I somehow doubt that this technique would work on any other door-to-door salesmen.