From what I understand, a failed steal attempt lowers reputation with the town the action took place.
However, this does nothing to placate a would-be or actual victim of the theft, regardless of whether it was a successful attempt or a detected bungled one.
I would like to submit for your consideration the following:
a) Regular failed pickpocket attempt to add an invisible timed flag to the thief that allows others to engage in combat with that character without guards' intervention, possibly with the exception of a 1000+ reputation thief character that would still retain the protection. The main issue seems to be low level characters to whom the reputation penalty is not such a great determent. The purpose of such is to allow the victim retaliation against the assumed thief. The flag would be on an also invisible timer (I think 30 seconds would work well, with the cavet that the timer does not decrease while the character is in combat), with the flag being removed when the countdown reaches zero. Neither the thief nor any other character should be able to verify the flag's existence, or remaining time for it to clear.
b) Critical failure pickpocket attempt to add a visible tag in front of the character's name (if possible, or some other means of indication - name in red color for the duration of the effect, perhaps?). The flag is set for longer, and even an Idolized character should not be protected by guards (I imagine critical failure to be akin to dropping the valuables in plain sight of everybody, with no question as to what occurred).
This alone should make anybody think twice about the consequences of a pickpocket attempt, without interfering with their ability to actually conduct such action. On the other hand, players that might otherwise have no recourse against the thief would not have both the ability to react to such an attempt (a), or be forewarned about the presence of a thief that recently failed at stealing (b).
Another detriment might be an introduction of Thief reputation that increases with every detected failed attempt, and affects NPC guards' behavior. An example would be an Idolized character with high enough Thief reputation being warned by the NPCs that any stealing attempt would result in severe penalties. Should the player ignore the warning, the result of a failed attempt would include, along with guards' reaction, massive reputation penalties with that faction.
From what I've witnessed (and, frankly, in that area I am sorry to say I had experience aplenty despite short play time), the issue is not the ability to rob other players as much as the relative lack of consequences currently implemented, in particular the ability of a victim or targeted individual to act against the thief while in presence of guards.
Please note that the above mechanics would not affect the actual viability of stealing as such, merely impart greater penalty consideration prior to deciding on such an act.
I imagine in a society as presented in Fallout, where the simplest things, or lack of thereof, mean death or survival, thieves would find very little acceptance.
