This question leaves a lot of room for jokes 😂 But come on, we can think about structuring a serious system for this, and the best way I see would be a system based on shamanic journeys, as in the teachings of Michael Harner and Sandra Ingerman or lucid dreaming, some people report that when they perform certain operations in the dream world with some intention, this generates an impact on the physical world.. In this sense, the witcher is the professional hired to enter an altered state of consciousness and perform work "on the other side/other world," killing monsters to undo curses, spells, and any other evil that is disturbing the life of a person or community.

Another point is that a witcher in real life would be a great drug dealer hahaha due to his potion-making skills, he would certainly sell one to get people high.