References and calculations
Just the act of asking for references will produce a reaction from the person doing the estimate, be watchful and observant to what that reaction is. As for the Manual J heat loss and gain calculations, these are time consuming and usually unnecessary for retrofits, however I am usually happy to oblige if the customer decides on using my company. After many years of pulling out old equipment and installing new, I can usually tell what a house needs enough to give a customer a good price on equipment. If, after doing the calculations I find I am off a half ton or a few btu's the price I quoted origially rarely changes. Additionally, I find an educated consumer to be the best customer, and will spend extra time bringing a home owner up to speed on anything they aren't familiar with.