Unfortunately Nutro is a pretty low quality food. Changing is not a bad thing, and in fact is a good thing as prolonged exposure to an ingredient can possibly cause allergies. Not to mention it can simply become boring. Kind of like eating chicken rice and carrots every single day for every single meal (as a human). Switching is just fine as long as the food agrees with the dog and some need you to switch them over over a 7-10 day period but switching foods is not a negative thing.
Also just remember, workers at a store are there to push the products they sell. Also most of them are not educated in nutrition for dogs or cats, many are influenced by the food reps that frequent the pet stores (I know Nutro reps frequent PetSmart and PetCo quite often). There's no "test" they have to take to work there, anybody can get a job there providing they pass interviews, etc. In fact, at ours, there's one girl that's 17 years old working there, not to say she can't be knowledgable on food, however it's more likely that she's spoken with reps, etc. My point being, is I would encourage you to do some research, learn to read dog food labels and identify what the individual ingredients are, what ingredients you don't wnat to see in a food and what you do want to see in a food so that you can choose for yourself.
Brands like Natural Balance, Wellness, Solid Gold, Orijen, Blue Buffalo, Innova, California Natural just to name a very select few are all good foods.
