Do you really think this is a meaningful risk here? Would be a huge hit to his reputation if he broke $2M and bolted. With a risk of $1-75 for most folks, that risk/reward ratio seems fairly trivial.
It's unlikely that Braff would "bolt" with the money, but I could imagine the movie getting canceled after the money has been spent, leaving backers with no movie and no refunds.
That seems pretty unlikely, and kind of highlights how this transforms the risks. If Braff funded it directly, his risk only pays off if he makes the movie and it makes enough money. While using crowdfunding, the backer's risk is only if the movie is not made.
