We had one of those that opened with a promise to save us $20/month on toll calls. We were surprised, mostly because our toll bill is only typically a few dollars a month at the most. Needless to say, he couldn't deliver on the promise.
...Probably should have tried to hold him to it...
We had a salesman from a power company door knock and promise us the earth. He was kind enough to write it down for us. When we stuck to our guns to hold the power company to the promises of their authorised agent. They came back with a $300 cash settlement for us to go away.
Not bad for 3 5 minute phone calls from the Mrs. Her brownie points definitely got a boost that day.