I feel like the solution of hoarding your local questgivers via claims is a bit silly towards the new players of an area, but as it is it seems it's the only real system to protect quest givers from people setting out to specifically sabotage an area's questing.
Killing a magical talking rock spirit or tree spirit should incur the wrath of either nature, or drop a badass enough scent that the players themselves can avenge their fallen tree friend with nidbanes. If you fuck a community's quest givers they should be able to rain nidbanes on your account (alting tree murder is too easy) or track you on any of your characters at the very least. Too much gain in the form of sabotage for very little risk.