I've been on both sides of that phone line, having worked as a telemarketer once by my own folly, and once by request.
When we were building House Two, there were certain outdoor lighting fixtures I wanted (read: pricey). With the kids in elementary school and activities (I was a Brownie leader), work options were limited. Working for Catherine, I could set my days and hours. I worked there only as long as it took to make the money for those fixtures! During that time I learned a lot about the character of people. I was always polite, so the reaction I got was pure "them". I usually started by asking for the person on my list by name, then identify who I was calling for, and asked graciously for a few minutes of their time. If nothing else, Catherine demanded that we be polite and respectful. And even though we each had an hourly quota, she did understand if we were detained by a lonely person who needed to chat for a couple of minutes.
I appreciated those who would stop me right away and ask to be removed from the list. I would thank them for being brief and tell them it would take up to a month to be sure they were removed (this was back in the late 1980's, so computers were still primitive). I thought they were the kindest of souls, probably treated everyone with respect. Then there were the ones who cussed me out, or slammed the phone so hard it hurt, or walked away with the phone set down on the table. They were the worst to get, partly because you needed to make an hourly quota of calls to keep your job, partly because you KNEW that person did not want to talk to you and you wished they had said that from the start. I always mentally pictured those people kicking puppies or grabbing lollipops from the hands of young children.
If you WANT "polite", BE polite.
Oh, and my stint "by request"? A year or two after I quit, Catherine shut down her own business to take over as manager at a different telemarketer office - in-house for an established service company. She called a few of her best back to help get the staff she inherited up to speed with her way of doing things. I knew it was a limited engagement. Since Catherine was nice to work for in spite of the business she was in, I helped out for a few weeks.