Government might insist on one central guild that self-regulates the industry. In my world the primary Kingdom has only one guild of wizardry. This is a collective of many small schools that teach magic. It pools their resources to provide library and material resources and helps enforce the reputation of magic-use. 

This is a direct response to earlier times when magic-users repeatedly tried to take over the State, had to be viciously repressed and were hunted down to near extinction. Therefore the only wizard guild that is allowed today is a benign, educationally based institution that welcomes all magic-users and will support investigation into illegal conduct by its members. Its independence is assured but its leaders must answer directly to the King or his local representative and are held accountable for the actions of guild members.