Ask HN: how do you pick a worthy developer from Odesk or other outsource site?

I have a project that I want to get done with, and it requires PHP and MySQL expert. I post my project at odesk and others, of course I got responses.

Now because my background is not in CS (I work as a Product Manager and in big companies, I don't have to go through this process when I develop my products and ideas as I have engineering teams at my disposal. Also my tech background is in wireless industry, not web 2.0), how do I interview and select qualified and worthy developers to build my project? Most applicants are from India or Eastern Europe. I am in bay area.

Thank you for your response.

PS: if anyone here is interested in working on my project, please feel free to response here and I will contact you. Thanks.