most telemarketers only make money when a deal is closed, i .e. they get paid on a commission. if im not busy, i will try to keep them on the phone as long as possible and ask the dumbest possible questions.
i had one on a few weeks ago for over 20 minutes then came right out and asked me "are you going to buy or just keep asking me questions"
otherwise, i found not answering the phone means they will keep calling back