Isn't killing them, y'know. A bit much for crimes like trespassing, theft and being disliked by someone who has enough money to convince the guards to keep them out of the way?
I wouldn't expect any DM to wantonly kill characters for extremely petty crimes, just because they're magic users. I would expect them to treat magic users a little differently to others, but the only time I'd expect a magic user to be put to the sword for something petty, is if the justice system in question was either corrupt, Evil or Lawful Stupid.