Presumably they do get some business or they wouldn't do it, but who's signing up on the doorstep or from a random phonecall?
If you knock on my door, I'm absolutely not doing business with you. Even if you're selling something I'm genuinely interested in, I won't be buying it from a cold caller. If you put a leaflet through the door, with a real , verifiable address, you stand a much better chance, I have bought from local trades that way.
I feel for the people doing this work, it must be a miserable way to make a living, but how do they make a living?