Eh. I'm no lawyer but ti doesn't take much to figure that promising x in exchange for money and reneging on x is tantamount to fraud.
The term 'fraud' is generally defined in the law as an intentional misrepresentation of material existing fact made by one person to another with knowledge of its falsity and for the purpose of inducing the other person to act, and upon which the other person relies with resulting injury or damage. [Fraud may also include an omission or intentional failure to state material facts, knowledge of which would be necessary to make other statements not misleading.]
You have to prove that they intend to break their word.
As an example, the author of a certain open-source non-linear video editor is, apparently, using his two successful kickstarter campaigns to travel to software conventions around the world instead of getting the NLE into shape to make basic edits. However, there is code in a public repository, so he can claim that he isn't defrauding his contributers, even though the kickstarter campaigns are his only source of income and these conventions and travel to them are not free.
That being said, Kickstarter is not a store.