The top Google links didn't mention Shakespeare's Shylock, which I always understood to be the origin. It turns out there is some disagreement between this origin and a German word.

http://observer.com/2003/04/national-review-and-shyster-heav...

I think that's an adjective form of shyster, someone who is unethical, especially a lawyer.

I was stumped on that term myself, but it certainly doesn't sound endearing. It felt dishonest to rip the last line from the passage though - as if I was trying to misquote him. So I left his comment in it's entirety.