I covered this towards the end, if the person logs off, the one who was trying to kill him gets a notification or something and he can go back to the assasin's house and get a new person. They could make it so you could kill the person that you're hunting anywhere they are, and as for the complaining, they complain anyways. Like when I'm streaking and i kill someone who's doing a job, they threaten to report me for interupting them(lol). If it really bugged them that much, they could just log off and log back on and they wouldn't be hunted anymore. Or when the assasin NPC that you talk to gives you the person, it sends a notification to the selected player asking him/her if they would like to participate.