Manipulative people do not understand the concept of boundaries. They are relentless in their pursuit of what they want and they have no regard for who gets hurt along the way.
Unfortunately, I’ve got one or more of these I’m dealing with currently. So I’ve hit the library and come up with George Simon’s book In Sheeps Clothing: Understanding and Dealing with Manipulative People. It is not a huge book, but manages to be quite comprehensive and helpful. First off he talks about what these situations look like, and then later he talks about what you can do. Here’s the brief list of how to handle these difficult cases, summarized from the book.