Don't most kinds of business require some capital to start?
So even with janitorial work, an educated graduate can turn it into a profitable business, without actually doing the cleaning himself.
Edit: his site is http://www.maidsinblack.com/ and he does a great job of documenting his startup experience step by step on reddit. If I find the thread, I'll post it here.
Anyway, this kind of business would have been possible in the past with local newspaper ads and the Yellow Pages.