So do they pay fair wages and do they pay in cash so the immigrants don’t have to pay taxes?
Depends on the company and the job. For example, the major oil companies require contractors to have a master services agreement to work for them. It requires contractor staff to demonstrate work and safety training, pass drug tests, etc., and that work is good money. Now a contractor may need to have a subcontractor do some occasional work, say use a backhoe or haul dirt. The subcontractor will invoice the contractor for the work, but with his employees that's where there may be a bit of exchange of cash for work. It all depends on the honesty of the employer.