This is sad to read. I am choosy with the clients I work with, and I think that's very important. If a client raises alarm bells for me early, I'll be even more diligent in making sure everything it categorised and spelled out to the letter, regarding the terms of how we will work together.
Also too late for you this time I know. But I really strongly advise not to do any work for free as a sample. If they want to see your work can show them a portfolio... If they want to 'test' your wirk in their setting, let them set up a small initial project.
Sorry you had this experience.
New! Stand out from the crowd by taking our gamified personality tests. Get started now by discovering the three tests available free of charge!