Dexter - did you consider that Dilbert isn't good at selling stuff so he tried to stick with the script, since he was told that it was foolproof? And now it's just me guessing but I don't think that there are exceptions on this script like "if the phoned customer is your mother, skip to section 2c".
We have a do-not-call registry in Australia where you can register your preference to not be annoyed by these parasites. Companies are heavily find for not obeying your wishes. This should be done everywhere.