As mentioned by others, the ethics guidelines are, for the most part, part of the Association of Realtors and their individual Boards of Realtors. The Denver Metro Association of Realtors covers a good portion of the metro area so I would start there. There are many real estate agents out there that are not members of their local board of Realtors so they are not bound by these ethics. Whatever you do, choose Realtor. That means that they are members of their local association, the Colorado Association and the National Association.
All real estate agents must follow the laws as set forth by the real estate commission (DORA). You can check there for any disciplinary actions taken on a licensed agent as well. But not all lisencees are members of the Associations we discussed above and don't live by those ethics.