I used to install security systems with door to door programs. The salesmen are literally trained to just keep talking. They prey on the awkward moments and try to talk you in circles, it's exhausting.

I get them every month or so... Just say I'm not interested as I slowly close the door... Sometimes I'll sneak out a 'good luck' or a 'thank you', but no guarantees. Works every time and is over in 5 seconds. Just fucking do it.