I have never had problems keeping this fish, assuming we are talking about Halichoeres chrysus - I have always kept them in groups (simliarly to the radiant coris, Halichores iridis). I have heard reports of them eating flatworms, and even the dreaded red bugs. They need a sand bed, and I have seen larger ones flip snails and hermits.
Don;t know why it would be labeled expert only, they seem to do great, assuming they don't jump out.