afaik they deal with this in a couple of ways:

• the first step is to go to the fair work ombudsman (this is a government department that handles complaints, fines and orders businesses to make restitution/changes to comply with the law on behalf of ordinary people. they’re free. we also have for example the telecommunications ombudsman, banking ombudsman, energy and water ombudsman, etc). proof required here is simply more probable than not
• not correcting systemic issues that form a pattern when they’re pointed out may be used as evidence in criminal prosecution. proof here - as it’s obviously much more serious - is beyond reasonable doubt, and must require dishonest conduct

so yeah, with regard to criminal conduct, repeated underpayment and patterns counts towards dishonest conduct and this criminal prosecution