We had these ne'er-do-wells at our door earlier this week, too. It was an aggressive, unpleasant sell: they claimed to be from "MoneyExpert.com" and suggested they came into my house when I said I didn't know my energy bills without checking. I refused, and then spotted that one of the "trainees" was happily testing his pen on my recently painted wall!
Needless to say I told them to go (a little more colourfully than that, to be honest) or I'd call the police. Didn't realise they were worse than nonchalant graffiti artists.