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Great point! You'd lose the collateral AND the remainder of the funds would be kicked back to the funders. If you make the collateral larger than the first distribution then it would make 100% scams impossible!

Since the project backers decide on the milestones, they have the power to make the stake equal to the first milestone. :)

this also is a good point, banks have operated this way for a long time. you must prove that the project is on course before the next stage of funding is released. good way to proivde confidence and protection to investors