Battles are going to be a little weird. How they are going to work starts off with the Level you are. If you are a much Higher level then the person you are fighting then you are going to have a higher chance in beating them.
If NPC A is Fighting NPC B [NPC A : Level 24 - NPC B : Level 12] Then unless NPC A lets NPC B beat him there is no way NPC B will win without some kind of help.
IF NPC B fought NPC C [NPC B : Level 12 - NPC C : Level 12] then it goes to the amount of Posts they have on this guild. So if NPC B has 400 post on the guild and NPC C has 261 then NPC B wins. But NPC B can always lose the battle if he/she wants to. Maybe it would help their story line they believe.

If there is any other Questions about this Please ask.