Spotting Scams, Feeling Stupid

This week, we're going to take a look at horrible job board experiences and at the end of the week, we'll hear from a writer who has gotten really great jobs and ongoing work through job posts. We'll learn how she spots the potential scammers. This was recently posted to Craig's List: "I recently replied to a craigs list posting looking for freelance writers. I got the gig and wrote the article. Now I cannot get the company to return a phone call. It's only been 10 days, but if by next week I haven't heard back from them, I will gladly tell the entire craigs list community the name of the place. The message here is: Get paid before you do the work. A lot of the companies that post here are small and know that you won't be able to dedicate the time, $$ and effort that it takes to track them done if they stiff you. If you've had similar experiences, let me know, because right now I feel stupid and alone."
Most of the companies that do advertise on these job boards are small, or they are start ups and we writers, as small business owners do have to take steps to protect ourselves. I've taken 3 jobs from job posting sites and I never take them without first checking out their website, calling to verify they're a legitimate business, doing a free phone number search to see where the phone number is registered and to whom. Talking to them also gives me a more secure sense. Also, my contract demands half of the payment upon signing. If the company wants the piece immediately, I direct them to pay the first half through paypal. If we have some time, I go ahead and tell them to mail me a check to avoid paypal fees.
What are some of the steps other writers take in doing business with new clients?