When your goal is to make a quick buck, tricking customers into signing deceptive contracts is standard business practice. These contractors will use a variety of tactics to trick you into signing early and if you make the mistake of falling for their tricks, you are the one who will have to pay.
Many homeowners find that their furnace or air conditioner is in need of replacement and they purchase a unit from the first company that comes along. This is not only reckless but it could also be disastrous. Everywhere you look you will find someone that is telling you to get multiple opinions before you replace the system.