We had a door to door salesman come up and ask to see are bill and didn't understand that we don't have it (we rent and the landlords does the bills). After talking to one of my other roommates for 10 minutes and her being too polite to shut the door, he came back 3 hours later!
I answered the door this time and knowing the voice my roommate came up and said it was the same guy. He kept trying to talk after we repeatedly said we weren't interested.
I shut the door on him as politely as I could. I don't mind door to door salesman, but when someone says no thank you, you don't come back less than 3 hours later!