The guild (ギルド girudo) is a network of vigilantes. It is too small to be a threat to the World Void Information Controlling Organization, and therefore its existence is an exception to the four agreements.
The nature of the guild is to spread useful information about bounties between vigilantes. Also, they pass a reward to those who for some reason cannot take it on their own, but they usually charge commission for doing this.
Ordinary people do not know about the guild’s existence.