Petco selling unhealthy fish?

I recently went to petco to buy my first couple tank inhabitants- A small red sea star, 3 little hermit crabs, a damselfish, an emerald crab, and a snail. At first everything was good- everyone was getting along. Come to find about a week later, and my starfish appears to be decaying. Her limbs are falling off, although nothing has hit her central disk yet. We went into petco today to find another addition to the tank(we didn't notice the starfish until after we'd returned home) and most of the fish looked super unhealthy (fin rot, disease- none of the fish looked good, along with seeing dead fish in a tank). This isn't the first time we'd spotted dead fish in a tank there. We decided to just get a piece of liverock that was in a tank with a healthy wrasse in it. Since I still wanted a fish however, we went to Petland to see what they had. The fish there looked significantly healthier and there was a bigger variety. Of course, that meant the prices were higher. I was shocked at the difference in the tidiness of tanks. I will not be shopping at petco for any more fish - its not worth it. I don't think saltwater fish are their forte.