You may laugh (or not), but alot of companies that use illegal labor, do advertise in the yellow pages (is nothing sacred?).
In my office, I'm one of the people who checks out our employees and contracters and subcontractors.
As I said earlier, most of them are immigrants.
Even some of the sub-contractors (who are independent contractors). There are alot of legal (and in a sense moral) obligations and liabilities that I work to take care of.
The immigrants I have working for me, are not underpaid and this is not a case of me using them because it would cost more for an American. I have been in the situation where I could have cut costs in a huge way if I looked the other way and let my contractors bring in illegals to do work.
I never did nor do. Its not fair to the American people or to the immigrants who come here legally to allow them to be undercut by cheap and illegal labor. Its also the equivalent of exploiting people in need to save money.
The immigrants who I do have who work for me, got their job mostly through referrals. i.e. "Friends of friends".
Unless the people/business your office hires are/is a corporation, don't you either have to pay their payroll taxes or issue a 1099 form every year? For your own household employees, you need to withhold or pay the payroll taxes for them.
To withhold or pay payroll taxes and to file the related W-2's 1099's etc., you need to know the employee's social security number (By "payroll taxes," I mean Social Security and Medicare taxes)