Disciple, The reason petstores get away with mixing a LOT of completely incompatible animals, is simply b/c shipping stresses them out, and improper care weakens them, and they don't have enough energy to fight with an incompatible animal until you get them home, and get them properly taken care of....
For example: Our petstore mixes Brown Anoles, Green Anoles, and House Geckos, normally, these animals DO NOT live in the same "section" of the forest. Especially since Brown anoles EAT green anoles' eggs, and geckos eat both kind of anole eggs. So these animals are all stressed due to close quarters (20-30 lizards in an enclosure big enough for only 1 of either kind) The stress of having the animal that eats your eggs jammed in there with you, and long shipping from being snared from your home tree.
I would be too stressed to fight someone I didn't like too!!