Look, The Player thieves cant attack you untill lvl 40 or 1 star trade. 40+ and 2+ trade stars they can attack you freely.
The NPC thieves will attack you anytime whenever you are in a trade but not in a safe zone. When you are lvl 20 and making a trade the NPC thieves will be lvl 16-->21. They are higher than you by a maximum of 2 Levels and lower than you by a max 4 LVLs ..... They are very easy to kill so do this
