Even her hu*****and earns cash income, he is unlikely to store the cash under mattress, there will be bank deposit, also the court will look at the contribution to the family, if he earned income and didn't contribute to the family, he is a negligent person and so has no claim on her contribution to the family. If he did contribute to the family, and doesn't report such cash income as taxable income, he is also screwed. So his choice is pay tax or pay family, both ways, he is in very awkward position now. If he choose to disclose the gray income, the court will take that into consideration as his earning ability. Even the hu*****and is jobless now, the court is likely to reward his child care responsibility based on his past earning record. Even with a minimum wage job, the court will reward 100$/wk/child as the minimum in CA, it is his responsibility to find a job and earn such income. If he misses payment, he will be forced to back pay by law. As soon as the divorce is finalized and recorded in the court, the court will notify state employment board, where all payroll service (e.g. ADP ) is obligated to garnish his wages based on the court notice to state and federal agency.
i.e. just like withhold income tax for government, the payroll service needs to take that portion off his paycheck before the ex-hu*****and got his final cut of the paycheck. I have seen terrible Chinese man to exaggerate his burden of financial stress by listing all sorts of job related expense and therefore tried to reduce his contribution to the family, the judge just questions why such careful book keeping doesn't have bank statement, doesn't have cash payment receipt. The Family court system deals with huge amount of such cases, the court is very experienced and fair to treat such cases. The family law is centered around protecting child welfare and wife.