A system that relies on common sense, trust and honour rather than explicit rules and authority is generally known as an "honor system" or "trust system". See: Honour System (Wikipedia)
In Nordic larps, much intra-character conflict is resolved using an honor system rather than rules and game mechanics. For example, a boffer fight will be fought until one of the participants decides that his/her character has been wounded to the point of surrender. The lack of formal rules makes the player focus on being seen as a good role-player by his/her peers rather than fulfilling the technical requirements for victory.
Although rules and practices vary considerably between Nordic larps and other larp traditions, Nordic larps have a general tendency towards honor systems, especially when compared to larps in most other countries.