Warning.....The caller will ask if you can hear them alright......If you answer "yes", they will use your recorded voice as if you agree to their sales.It will be used against you in the future. I recently saw a report of this on the nightly news.
SPAM - The caller, usually "Emily" will ask if you can hear them alright - prompting a "yes" from you, and will then apologize for not having her headset in. There's been speculation that by recording you saying yes that the company can scam you later. Snopes.com refutes this as a viable outcome but it's concerning and annoying.