After reading the entire thread (which was very amusing) i really got to know few points which writers and their clients face but the only option available to you is what you are doing and as others advised. Go with the sample and then shorten your list of available writers. then give a small paid competition to all your shortlisted writers. Always decide two three writers and sub divide your project. Then work with them on regular basis and you will soon realize which is the best for you. The process may sound lengthy but there is no risk of loss in it. Trust me !!!!
This sounds like excellent advice. And just to think, only three pages of message board posts to come to this conclusion