You really want them to pay? Ask them to complete a contract for the services, you are very interested, but would like to read about it first. The packaging, disclaimers, forms, will make for a very big envelope and consume lots of time for them. When you get it, forget to complete the important parts, legally binding, then send back. Then they will call you again, apologize for the mistake, have them send it again, repeat process until eternity...
Good idea! Letterman did skit on this. Guy invites a telemarketer to dinner to talk about their deal. He gets there and punches him out.