When I freelanced, I evaluated clients on three criteria:
* had I worked with them in the past?
* did I know anyone who had worked with them in the past?
* everyone else
If I trusted them or people who had worked with them, it made the engagement easier all around (though you still need a contract!).
As far as finding new clients, I relied on word of mouth, which probably didn't lead to as many opportunities as would have occurred if I was more active in various communities, but I was ok with that at the time.
Also, I wonder what the author moved on to?