The owner should always be held liable if one of their workers scams an amount over the amount they themselves were insured for (if the worker is unable to/refuses to pay back the amount scammed). It is the owner’s fault if a worker is even able to deal with trades above the insured pot. If the worker wants to handle trades of higher value, he/she/they must increase the insured amount they initially paid to start working.
If this is too hard or difficult to understand, then you shouldn’t be operating as an owner. This is basic knowledge for trust-based business practices.