interested in your product .. then don't knock on their door
If I answer the door and you try to sell me something I'll say not interested. Thank you and then shut the door.
I don't care if they think it's rude. I've been in sales. I know they're trained not to take no for an answer and I really don't want to waste anyone's time.
I see what the op means about not answering the door. But homeowners shouldn't have to be ever vigilant that potential visitors might be selling something.