Well, green treefrogs are wild caught and are usually loaded with gastrointestinal parasites. You mix that with the stress of a new living situation and possibly poor husbandry skills, and the frog will most likely die. Its really a good idea to have all your frogs dewormed/treated for GI parasites, even if the pet store says it's captive bred. Unless the pet store practice severe sanitary protocols or only deals with captive bred animals, there is a good chance that there will be CB animals being infected with GI parasites whilst in their care.

PS I have had my green treefrog, Hyla cinerea for around 4 years now.