A good editor isn't someone who rewrites the text. A good editor hears the writer's voice and helps that same voice be heard more clearly.
Many new writers think editing is the same as proofreading. Proofreading is necessary, but editing is also about the structure, rhythm and logic of the text.
Before handing your text to an editor, write down what you want: the level of editing, how far they may intervene, and the parts you're worried about yourself.