I'm a big fan of exile. Not really possible in today's world, but being kicked out of your community must have been one hell of a preventative measure.
Regarding your other questions... My line would be drawn by how badly I'd fare before a powerful state that would punish me for my just retaliation.
I probably would hold someone in my basement if they scammed me $100 until they called someone to pay me back. I wouldn't kill them of course. I might even forgive someone who robbed me of $100 because they were in a bad situation.
No real answers for me. I'm just wary of hard and fast lines drawn.