In Fallout 4 (PS4), every now and then, when I'm trying to steal something, even if I'm Hidden, sometimes the owner still knows I stole from them. This happens even if I am completely Hidden and out of the line of sight. Anybody know why and how I can avoid it moving on?
Yes, as @Nolonar mentioned in comment, it depends on many things like: worth and how many objects in one turn if pickpocketing, on target level, his and yours Perception level, environment and daytime , your stealth skills, other NPCs around etc...
In case of looting diamond apartments timing is key, vendors homes when they working, upper class while they drink at bar. Recommend crouching before enter and when exiting, also good way in are roof hatches. With hyped thief skills is possible to steal fusion core from raiders or BOS wearing Power Armor, without it they exit and you can steal whole power armor.