I hired someone from one of these threads a few months ago. I chose them over other candidates based on a strong “portfolio” web site, showing me the person understood their code existed to serve business values (not the other way around).
1) Some amount of professional experience in the technology we were looking for a contractor in.
2) An attitude that boiled down to “I write software to fulfill business objectives.” (The opposite attitude is what I characterize as the “hipster coder,” who says “I couldn’t possibly work on your legacy system unless you agree to rewrite it from scratch in $hot_new_stack.” Yes, I have literally had a contractor tell me that before, about a webapp based on a 5 year old front-end framework.)