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You are missing the forest for the trees -> there will always be some fraud, and thus a devision must be made regarding who is responsible.

Furthermore, if the bank don't suffer from faud, they have no incentive to fight it. So there will be no effective securiry

You can just have a voluntary system wherein people decide beforehand how funds are distributed in the case of fraud.

That doesn't necessarily require a third party like a bank to surveil and supervise every transaction.