We use Royal Canin and are happy with it, but I wouldn't pay too much attention to what Pet Store workers have to say. I don't think it's an allergy, food allergies usually don't show up on a puppy, and most dogs are NOT allergic to corn, its called a common allergen because it's in so many foods not because of the number of dogs allergic to it. What do you mean by dander? If your dog is showing white flakey skin, it can be that you are using a too harsh shampoo, not rinsing thoroughly and not using a conditioner. Remember conditioners are helpful, because they condition the skin as well as the hair. I really believe the Biogroom Shampoo is one of the best shampoos for Yorkies, you can get a free sample packet, by requesting one on this website under "contact us." Don't forget the products are very concentrated and you MUST dilute them.
Bio-Groom - Exceptional Pet Care Products for Over 30 Years