Duty Of An Agent

I have a client that fell victim to an unscrupulous realtor.  Basically the client was pursuaded to purchase 3 homes as investments which would be flipped within a couple months.  The problem was that it happened to be end of 2006.  There are other details involved, but my issue is this; I want to examine the standard of care for an agent.  Hopefully some agents who view this can express what they consider to be their fiduciary duty when advising a client.  At what point should a realtor be held liable for their recommendations?

As a follow up on this issue, what should be considered reasonable efforts in promoting a listed property?  Is a single picture on the MLS sufficient?  what response time is appropriate in responding to inquiries?

My goal as an attorney is to praise the good and admonish the bad.  I think in doing this, the real estate industry is well served by protecting the reputation of the profession.  Hopefully i am not alone in this view, but would love to hear feedback.