What an unusual question. I even used to listen to telemarketers, back when there weren't so many of them. There was one man I used to work with. He was very smart and always assumed you knew what he was talking about, even when he left out important things. I think his brain went too fast for his mouth. He would get upset if you asked him to repeat something he said, or acted like you didn't understand him. Everyone knew he would never ask your opinion, so most people would often just nod. He was a character. But he was a pretty good guy.
I never pretend to listen - although like Nancy I have done some 'nods' when I probably should have done the opposite only due to the fact I couldn't hear what was being said
When I'm on the phone with my long winded sister-in-law. All I have to do is say, "Uh-huh" every now and then. Bless her heart.