Ignoring fraudsters will only work if that causes a cost to the fraudster bigger than the gain by double spending. Basically you will have to use key pairs tied

Ignoring fraudsters will only work if that causes a cost to the fraudster bigger than the gain by double spending. Basically you will have to use key pairs tied to natural persons. If there is any anonymity or pseudonymity the fraudster will just generate a new key pair and double spend again. How does this system guard against that ?