The methods have changed over the years and I think there are far fewer real cold-call sales and far more fraudulent ones now – maybe the former dissuaded by the latter.
If someone tried to sell me something over the phone – typically a phone company wanting me to change to it – I would insist to the caller that I want all the information he or she has given me, the T&Cs and the contract forms, in writing, before I decide whether to take their "offer". They didn't like that; perhaps thinking I was calling them liars. Maybe they were genuine, a decade or more ago, maybe they were liars – these days far more likely the latter.