If traditional feng-shui hadn't improved the life for the Chinese people throughout history, chances are it wouldn't be around today. Find a practitioner who appreciates and understands the culture in which feng-shui originated. You don't need to be Chinese to practice feng-shui, but to practice it well, you should be very familiar with Chinese culture. I've also found that most of the best practitioners have undergone formal training and apprenticeship and can tell you the origins and history of the school in which they trained. Find a feng-shui practitioner who will agree to explain the rationale behind every recommendation he or she makes.
Good advice is based on understanding principles rather than following set recipes.
Just as a doctor should be able to explain to a patient the causes of illnesses as well as the rationale behind the prescribed remedy, a competent feng-shui practitioner should explain why certain building sites are desirable or undesirable, why some houses are conducive to the development of positive energy while others carry destructive energy, and why he or she is recommending certain improvements. Learn as much as you can about feng-shui yourself. If you know the principles of feng-shui, you can ask good questions of prospective consultants, evaluate their answers intelligently, and make your choice accordingly.