I think that should be another job for the players of planeshift.
Think about it, with npcs, you cannot argue your way through, (speaking from everquest experience), if they are hostile, they will attack you no matter what, or the opposite.
while players, (by the way, there could be guilds that can take up these roles), could have certain rules about who may pass, and also it would be easier to negotiate with players.
for example if they see that the person who is passing is packing maad expensive gear, they will stop and rob that person. but if the person is poor and not wearing anything, they will hep him, maybe give me a beer.
actually now that I think about it, if the npcs could be programmed like that or even better, it would be much cooler.