The easy way is to not promise any rewards that depend on completing a complicated project. Like, send people a novelty pack of gum and also figure out how to get them a copy of the game if it happens to be completed, just don't promise them the game.

Realistically, Kickstarter is a store and people won't pay if they aren't getting the result of the project.

Well, this discussion is about people who paid and aren't getting the promised result.

I think Kickstarter is neat, but I think people should probably approach the claims of the typical project with quite a bit of cynicism. That means (as a backer) not treating it anything like a store.