Gah! I’m sorry you’ve had so many of those experiences. I’ve had a few.
I’ve been freelancing for 30 years, 20 of them online. For me, contracts are useless, none of my clients are in the same country as me.
10 years ago I did an experiment. Took my website offline and only worked with referrals. Of course, only my best clients gave me referrals. For me, that got rid of all the “wrong” clients.
What I discovered along the way is that the best clients to work with are the ones I don’t need a contract with. We do them anyway, but they don’t mean anything because, duh, different countries.
Here’s hoping 2016 brings you better clients!