I've never done that, but I think a lot of telemarketers earn their bad reputation. I had once moved and gotten a new phone number and for the first few weeks I would come home from work to messages from some collection agency looking for some woman. I decided to call them and tell them they had the wrong number. The guy was a total dick to me and accused me of being her boyfriend and covering for her
I also had a guy call me and offer me a free prize with no cost. Then he went one to tell me to get my prize I had to order something. I told him that if I had to buy something it wasn't free and hung up on him. He actually called me back. I had never had that before.