When choosing a contractor to work on your home be sure that the person you choose is qualified to do the work.  If you are choosing someone to work on Electrical, Plumbing or AC they should carry a license through the state you live in to be qualified to do the work.  You can go to the state website and type in their name or the business name to double check and make sure the person you choose is indeed qualified to do the work.  Trades people are required by state regulations to keep their licenses up to date and to take continuing education every year to stay up to date with the changes in codes.  If you live in a city where a permit needs to be pulled to work on your home only a licensed contractor will be qualified to pull such a permit.