Oh, these are all such good stories!
I usually have 2 approaches, depending on my mood:
1) Just yell as loud as you can "NOOOOOOOOO !!! I DON'T WANT TO BUY YOUR CRAAAAAAAAAAAPPPPPPP!!!!!!! LEEEEEAAAAVE ME ALOOOOOONE!"
It's very annoying.
2) "I'm not allowed to talk to strangers on the phone...