Every bounty hunter system is fucked, regardless if its NPC controlled or player controlled. You can always get around it with using alternative characters. We got a shitload of ideas for FOnline, but most of 'em have been dropped, due to the possibilitie to abuse them with alts.
Agreed, group of people can easily exploit this and similar systems.
From my view you can't prevent damage that other players can do. Best thing is to avoid them or you'll get owned. Theft in NCR for example, even if you kill the thief you can't get your stuff back.