InfoWorld: Clients or Grifters
The gist of the article though is that as soon as you impose tighter controls/credit terms the scammer gets flustered and runs away.
I know a few companies who run on a credit of trust, if you are brand new, you get no credit, so you start with the most restrictive terms.
If you are a known, reliable client, you get the more lenient credit terms.
The scammers balk at the terms, the cheapskates who will nickel and dime you to death decide to leave early and the genuine stay behind to do business with you.