I've had quite a few on the phone/at the door and I honestly don't mind them trying. I like to be polite and will generally wait to say "not interested" at the available opportunity.
But what really, really winds me up is when they do really staged "Yes" questions.
"This is just a terrible problem, isn't it?"
"£2 a week seems reasonable to help, doesn't it?"
Oh fuck off. Is it just me who gets so annoyed and thinks these "leading questions" are really them saying "You're so stupid, if I just get you to nod your head and agree with me you'll do anything I suggest." 
I know that it's a recommended selling technique and lots of people use it, but the main people who pitch to me are chuggers and it's only them who I notice it with. It just gives me the rage.