The misanthrope in me has almost completely taken over when dealing with incoming sales calls, and I've almost completely abandoned the idea that anyone calling me to sell anything is worthy of the "humanity" label.
The moment it's clear they are selling something (it's usually pretty quick) the reply is "fuck off, never call this number again, and go fuck yourself" then I hang up and block the number. I only wish I could be vengeful in response and actually retaliate in some meaningful way to those that are particularly annoying or persistent.
The same applies to door-to-door sales people, moreso to door-to-door missionaries.