I used this avenue in 2003, they even turned it over to one of their attornies who was unable to collect. He said going to court would be my only avenue.. He thought my chances of winning in court  were very low since I didn't have a signed contract with her.
I chose not to sue because I would have had to shut down my office and fly to Georgia for the trial.
So Dun and Bradstreet put it on her companies credit.
I use to own a nationwide company and we worked for Banks directly and I know that they check out your company credit before giving you work, so I felt pretty good about that.
Now I have a new policy, $300 is the most I'll allow a new client until I see regular payments.