If they have a long spiel and dont let you get a word in edgewise
I dont hang up but just put the phone down and see how long it takes them to figure it out.
I dont really care what their personal situation is, I dislike going to the phone only to have a phony charity, survey or marketing call waste my time. Sure I can let the phone take the msg, but on the other hand
there are far more telemarketing calls being made now than there were 10or 20 years ago - back then when the phone rang you were far more likely to answer and know that its someone you know.

now with call display - you can identify the # and not answer - they sometimes get around
if I happen to get a telemarketer when I answer I ask if its a sales call, I dont do surveys either.
but one of the best ways to deal the is to say 'you just called me yesterday'.