The list that the NWFA maintains at
http://www.woodflooringinstallers.com/ includes anyone that is a NWFA member, although they do designate which ones are NWFA Certified Professionals. So just being on that list doesn't guarantee anything. Stick with the designated NWFA Certified Professionals. Other means of finding a good contractor: ask your friends, neighbors, co-workers - expecially the picky ones - who they would recommend. See their floors. Make sure you are getting the same mechanics, especially if you are hiring a company that sub-contracts out the work.