Many people have front door intercoms and doorbell cameras nowadays.
I suggest connecting these to the Internet, and letting people in the same neighborhood/apartment building connect theirs to a sort of social network for doorbells.
Then, when somebody comes around knocking on doors advertising something, everyone except the first two or three households they visit can get an early warning of who's about to come to the door. (Just one wouldn't be enough to detect the pattern.) As well, the people visited can submit their impressions of the person for the neighbors to read.
Also, if you have a camera, it can compare the person it sees to the pictures taken by the neighbors' cameras to be sure you're not inadvertently ignoring your friend who happens to craunch your marmoset while a solicitor is about.
ETA: And you can share reviews of people who come to your door. And it records video for the purposes of security and sharing funny incidents (which is facilitated through its own social network, or you can post to YouTube or whatever).
38/241-- notexactly, Jul 05 2017 "English As She Is Spoke" https://en.wikipedi...ish_As_She_Is_SpokeAn invaluable reference for any visitor to Tibet. [8th of 7, Jul 05 2017] Make them pay! Parrot_20DoormanDoorbell relayed by 3rd party [Zimmy, Jul 07 2017] Vaguely related, could benefit from this idea .... Trick_20or_20Treater_20Non_20Repeater [normzone, Feb 05 2018] //your friend who happens to craunch your marmoset// - I assume this is a euphemism for something unimaginably obscene-- hippo, Jul 05 2017 Strangely, no. It's a direct quote from a very old English-foregn phrasebook entitled IWRC "English As She Is Spoke", compiled by a man who didn't speak English, but did own an Italian(. ?)-Portuguese dictionary and a Portuguese-English dictionary …
Hilarity ensued.
<Python>
"I will not buy this record, it is scratched".
</Python>
<later>
french, not Italian.-- 8th of 7, Jul 05 2017 Ah yes - I knew of the book, but not that phrase-- hippo, Jul 07 2017 Is there a term for when you thought you'd posted an idea under one title, but you realize you actually posted it under a different title, so you update the title to reflect what you thought you'd titled it, and then you add features to the idea that are suggested by the new title?-- notexactly, Feb 03 2018 The Ring video doorbell does have a social feed which primarily focuses on showing weird characters that walk by peoples doors-- theircompetitor, Feb 05 2018 Try not to take it so personally - it's not like they're just looking at you. Mostly you, yes, but sometimes other - less weird - people as well.-- 8th of 7, Feb 05 2018 random, halfbakery