When choosing a window contractor make sure they are licensed & bonded. Check out the professional organizations them below too. How long have they been in business & what type of training have their installers gone through. Get references and check them out. Quite simply make sure they are professional, do they show up on time for appointments, are they respectful of your home, do they give you a written proposal and never give them money up front. Also, check for complaints from the BBB or your county consumer protection.