Yup. Never answer the door. I always make people talk through the locked storm door. Glancing at them then the no solicitor sign and back and forth.

On a different note. I work residential hvac. People call us out we don't do surprise visits. I call when enroute, park in front of their house with a well marked company vehicle, walk up with company apparel and I still get asked for company ID. I do NOT mind this whatsoever. They're about to let a stranger into their home. I have one customer that requests me specifically yearly for maintenance on her furnace. I follow the same procedure mentioned above, she knows me by name and greets me at the door. And still asks for ID.

Moral of the story if they are supposed to be there, make the, prove it with ID. If they aren't tell them to leave a business card in the mail box and call them back if you so desire.