Witchers are raised and trained to be monster hunters. Once they training is over they leave Kaer Morhen (or whichever other strongholds they held in the past) and it's up to them to make their living by killing monsters.
Not an easy life. Even in the story "The Limits of Possibility" we see how the town folks start to split for themselves Gerald's possessions because he is taking "too long" to deal with a monster (and they believe him dead).
I remember from reading the first books how much Gerald (and probably any other witchers) was told to deal with monsters and not to deal with any other affair, but it seems that once their training is over is pretty much up to them to stick to the "witcher code".
Are there any known witchers that said "enough is enough" and "rebranded" themselves to any other profitable profession (such as assassins, bodyguards or sellswords in general)?