Amazon definitely will have a fairly decent argument that it wasn't a protected trade secret. Typically using an NDA (nondisclosure agreement) as means of protection is fine. But, millions of users who can sign up pay paying a token amount and then click a button or two? NDA might not be enough.

Indiana's trade secret has to be "the subject of efforts that are reasonable under the circumstances to maintain its secrecy." But it doesn't have to "extravagant" effort.

But notice that "under the circumstances" is included. If I were angies list, I'd say that they did all they could.