This does not stop them, but it slows them down. As they start their spiel, I ask if they can just wait amount while I time the hear down on the stove. Of course, years ago this was more effective because both parties had to hang up to clear the line. After about a minute, their line clears. They are less likely to keep you on a "try again" list IF YOU HAVE WASTED THEIR TIME. I learned to do this when they would call my business interrupting my helping people actually wanting to buy something.