I agree with the advice to answer the door and tell them no thanks, you’re not interested.
And why not say it nicely? I can’t see how closing the door in someone’s face without a word accomplishes the goal any more effectively than simply saying, “No thank you, we're not interested. Please don’t call again.” I feel the same way about phone solicitors. I don’t have to answer the phone, but if I do, I don’t just hang up on a human (fortunately, it’s usually a recording) or, worse, blow a loud whistle or something.
I mean, this dreary job is probably the best one that this person could find, and they don’t get paid much, at that. We all hate being interrupted by sales pitches, but I don’t think it justifies being rude and even mean to them.
These are particularly stressful times. We can help by being kind.