In the end it comes down, that these kind of bounty hunter mechanic doesn't work in a MMO. It's better to leave it up to players.
It's really possible that it doesn't work in FOnline. I mean, if someone sets a bounty on me, I eventually get killed... So what ? I will respawn a few minutes later, and will only have lost my current gear. No big deal, and each days, dozens of players are killed by player killers for the exact same result.
What about paying X caps on someone's head, and this person will have unavoidable encounter (or may be they will come even in city, probably, only unguarded) of Bounty Hunters (NPCs). Thier strength (NPCs+equipment) will be totally equal to X caps. I mean it'll be the same if you hire merc and buy a weapon for them.Edit: they will hunt him till he die in THIER encounter by them, if he escape an encounter, they will meet him again after some time, till he die by thier hand, or, atleast, in encounter with them.
Also some time lock to prevent putting bounty on someones head over and over again.
Since when is Redding sheriff badass raider who gives a fuck about people?