My daughter had a cold caller about installing a conservatory onto her home. The usual thing, we were in your area today and noticed that you don't have a conservatory and we are doing a very good deal if you sign up within the next 48 hours etc. My daughter played them along and said she would be delighted to have a conservatory built onto her property. She let the person go on for a good 10 or 15 mins before she asked him if he could confirm that someone had indeed seen her property then could he answer a question? Of course was the answer. Daughter then asked him when they had developed the ability to build a conservatory onto a flat? "You b***h!" was the reply before they hung up. As my daughter said "Well mum it's their money they are wasting and they have wasted enough of my time!"
Sometimes her partner, a former police officer gets the calls. He is always very polite and says "Oh thank you for calling, your just what I need. Can you hold on for a second till I get a chair to sit on?" He then goes about doing what it was before they interrupted him. Make a coffee, read the paper, watch the TV, play with his son etc before he returns to the phone about 5 mins later. If they are still there he quietly puts the phone down again and goes back to it 5 mins later again before hanging up. They very rarely get calls of this nature now and SIL believes that they communicate with each other and are blanking his number from their list.
I know these people need a job but, THEY choose to do this type of job so I am afraid that I don't have a lot of sympathy with them when they get SIL on the phone.