i asked one petsmart employee what they feed their snails and she said that they eat the algae from the tanks. if they have had them for awhile they may have starved. at petco they don't turn their nerites over when they are upside down, which is a death sentence.not sure if they are aware of the problem or if they just don't care.
I used to work at Petsmart a few years ago and associates are not trained hardly at all in the proper care of aquatic (or birds or reptiles/ amphibians or hamsters, etc.) life. My guess is they are unaware that this is a problem for the nerites. We were never told to give algae pellets to the snails when I worked there, but I snuck them some anyway. Management is a huge POA there for lower employees. Such a sad situation corporate pet stores have become.