You should remember that the rewards are not supposed to be the main goal of a Kickstarter project, but more like an appreciation token for your donation.
And, to reiterate, I am just thinking of a reputation-based system, this more or less being an economy of goodwill. Kickstarter has so much clout and utility that the prospect of getting blackballed or receiving a poor public satisfaction index them could be a huge deterrent by itself without the need for any legal and consumer-advocate action to be taken.