Well, a more practical solution might be to approach the store's owner or district manager. Explain to him/her that the store which is displaying 'sick' animals is giving the public a 'bad image' of what a 'good' pet store is supposed to look like. Tell them that you have some suggestions to 'improve their image'. If you use terms like these they should be willing to do something. Also, if they take better care of their animals, more of them will survive and need less medical care; therefore saving the company money and increasing profits.
Offer easy to follow instructions on the proper care of the species effected. If possible, print some care sheets from the internet and take them in with you. Be courteous, and don't assert blame on anyone. You want to sound helpful.
Follow up with them in a week or so and ask how the animal is doing. If there is not any improvment, or you think the snake may need medical attention (which it probably does) you may want to report this (it IS a crime) to a Humane Society or Animal Welfare organization in you area. Call the police (non-emergency number, of course), and explain to them you are witnessing animal neglect/abuse/etc. By law, all complaints have to be responded to by uniformed officers if requested. Just having the police show up and discussing the situation with the owner/manager can be embarassing and scary (when speaking of fines, imprisonment, shutting down the store, etc.) enough that they may want to listen. If you are an extreme individual you may call for a boycott. Boycotts are perfectly legal so long as the protesters are not on the property of the store and aren't harrassing the customers. The purpose is to educate, and when possible divert those consumers to another place. Good luck and keep us updated actions your taking!