How often do you let people take advantage of you? What about governments, presidents, politicians? Where do you draw the line?

I've lived in France where I got chewed up and spit out for the first six months.  Some French friends explained how things worked and after a while I perfected not being taken advantage of.  It's stayed with me and I have to say surprised some people who haven't realised that I have this errrrrm characteristic just under the surface.