I worked in the international education industry for the Queensland Government for around 30 years. Many students are obliged to work due to lack of financial family support despite having to show financial statements to be self supporting This was easily fixed by the movement of money -at a charge- from lenders accounts,to show temporary credit where there actually was none.
Usually they work in hospitality- hotels and restaurant kitchens for cash. I had cases on 10% attendance ( minimum requirement 80%) and doing my best to get their visas cancelled for non compliance- while at 'war' with immigration lawyers representing them.

I would conservatively guess 10-20% would already be working somewhere.
The main offenders were Chinese and Brazilian but not limited to them.