What flaw in the fugitive slave law of 1793 kept it from being effective?

This painful law of the past, put fugitive slaves in danger (for life) of being captured again, and also said that children born to fugitive slave mothers, would be owned by the mother's dream, living as slaves throughout their lifetime. The northern states, to protect free black Americans and refugee slaves in the north, created laws that would prevent them from being abducted or recaptured and then enslaved legally. These laws were known as "personal freedom laws" and asked the slavers and fugitive hunters to give sufficient proof of the truth of their captures. While the southern states demanded their right to recover fugitive slaves, in the north, the states were demanding their right to protect their free African-Americans, so that they would not be kidnapped and sold as slaves.