Electricity and gas, the “take it or leave it” offer from the call center. How to understand if it is convenient for us and the tools to defend ourselves

A call center operator calls us to present us with an offer “only for us” and “only for a few days”. He shows us the price per kilowatt hour (or per cubic meter in the case of a gas offer), any welcome discounts and maybe even what will happen in a year, when the promotion expires. The proposal seems interesting, so we ask to be able to receive it also by mail to discuss it a bit.