the name apple snail is used for a variety of species in the Ampullariidae family of snails. chances are, if you bought a snail from a LFS, its probably the pomacea bridgesii and sometimes a pomacea canaliculata, which eats plants. i used to have three pomacea bridgesii and although they ate algae, they left a lot of poop.
best chance of getting what you ordered online is to use reputable sellers and online vendors, such as aquabid and so forth.
snails and shrimps would be a good choice.