I feel your frustrations. I have an unlisted phone number so I very rarely get telemarketer calls anymore unless they are computer generated. Well worth the fee the phone co. charges. Also I live alone and work from home. I get a lot of door to door salesmen, politicians, and kids doing fundraisers. I do not answer the door unless I am expecting someone. I have instructed my friends and neighbors to call first or come to my back door.
The police officer who came to my door at 3:00 am did not appreciate this however and just kept banging on the door.