Maybe I don't read the right journals, but I have never seen a guide to getting rid of unwanted cold callers on the phone. As I am frugal and seldom exposed to hard selling techniques, I therefore have to rely on strategies derived from a previous age.
In the 1980s, when unemployment was even higher than it is now, young people sometimes came to the door to ask if I would 'sponsor' them by buying a fire extinguisher or other durable commodity. My reaction was to invite them to sit down while I explained Adam Smith's distinction between the functioning of a market economy and that of the social order.
On Adam's account, markets can benefit all who take part in their processes of exchange of money for goods and services, without any one having any sense of responsibility or obligation towards each other. Societies, on the other hand, need moral standards, communicated through cultures and practices, to achieve fairness between their members.
The idea of 'sponsoring', if it belongs anywhere, is appropriate for the moral or social sphere. If markets and capitalism functioned to the benefit of all, as Adam claimed, then I should want to buy the fire extinguisher for its utility, not to save the salesperson from destitution.
I found that this always caused the rapid retreat of the commercial apprentice, and that none of his or her colleagues called in the immediate aftermath of the encounter. Whether this was because the unfortunate explained Smith's theory to the others, and convinced them of its validity, I do not know.
None of this seems to apply to the case of telephone cold calls. Perhaps I am paranoid, and too much of a technophobe to know how to check this out, but I have always imagined that many of these would allow the caller, in possession of some sophisticated device, to gain access to various bank accounts and pensions of mine if I spoke for more than a few moments. I would hardly get beyond the preliminaries of Smith's Theory of Moral Sentiments before these were completely stripped out.
So I am reduced to the very crude resort of saying, 'I am a police officer, and I only speak to criminals when I am on duty'. It seems to work.