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The best way to avoid having a picky eater is to reduce or eliminate treats, never feed table food, and choose a food and stick with it. Put the food in Alvin's bowl and leave it for 20 minutes. If he doesn't eat, pick up the bowl until the next meal time. Don't offer Alvin alternatives, otherwise you are training him to hold out until he gets the "good stuff." Healthy dogs will not purposely starve themselves.
Sometimes a food change will help, but constant changing and offering more and more alternatives will only make the dog pickier.