This is not really a strict and rigid set of rules, but moreso a set of best practices along with justifications that explain why the field generally decides a certain way in certain scenarios.
After all reputable professions want to make sure that they treat customers right and they want everyone in the field to make a good impression. Think about how people feel about certain professions such as bankers and journalists. In some cases a bad impression can hurt the business of all people in that profession.
These rules change in accordance to the many factors that affect the discipline, such as changes in societal perceptions and new research in the field. So what about the field of psychic readings? Do psychic mediums have a code of ethics that governs what they do? Click here to find out.