That is the fastest and easiest way to handle this. When I tell people that they often ask me to give them a my price and sometimes I will get the work anyway. If they are trying to get me to install their water pump or heater core for example, I try to educate them on why that is not a wise thing to do due to the minor savings and future labor warranty issues. Unfortunately, some people are so fixated on but I have "a lifetime warranty from Autozone" on the part they don't get the labor warranty issue.