If the money could be kept in escrow and only released partially as certain milestones are reached (with reasonable targets), that may also help reduce the abuse. For example, there is no need to give someone $1,000,000 in one lump sum the minute their funding campaign has concluded.
Let's say I was building widget X. I ask for $100,000 and get funded to $200,000. Great! I've met my funding goal and then some. Now I have 4 steps in my project... getting PCB designed, then maybe getting parts, and then assembling/testing widget, and finally shipping it out. You need certain amounts to get to each stage.... Why give the person the full $200,000 when all they needed to get funded was $100,000 which is what was asked to begin with? And even then, why not parcel it out in chunks that are appropriate to the amounts needed at the various stages?
There would have to be an independent review board or perhaps some representatives from the crowd-sourced funders to evaluate the stages to make sure things are on track.