I go one step further and tell them I don't talk to unauthenticated callers, ask them for a reference number and an published return phone number that I can aut

I go one step further and tell them I don't talk to unauthenticated callers, ask them for a reference number and an published return phone number that I can authentic using the usual methods (website, advertising material), explain to them that unaurhticated / cold calls are unethical, and then end the call.