In one of my campaign worlds the assassins guild was run by a church; you had to pay once to kill them, and again to make sure they stayed dead :P Introducing

In one of my campaign worlds the assassins guild was run by a church; you had to pay once to kill them, and again to make sure they stayed dead :P Introducing magic, or any kind of efficient machine or analog for modern medicine that might appear as magic in a fantasy setting means you get to throw out most of the rules that are learned from historical observations, except where you base those lessons learned on post-industrial revolution studies where the availability of electricity and modern industrial tools haven't been made readily available to developing communities and countries.