I too am in a slightly different position, because of the type of nonfiction I write (knitting books), which need to combine technical accuracy and factual/historical accuracy. At the research stage, I contact people who appear to have expertise or experience I feel I lack, to inform my content. My publisher hires an editor (either a project, technical or copy editor) knowledgeable in my field so that the editor can comment both on accuracy and on whether the material is understandable. In addition, my editor herself knits, at a level consistent with the intended audience for my books, so she can accurately comment on the content and the writing. I never give my manuscripts to another expert to read. I am an expert and, like Escritora, I'm contracted to write about my own approaches, solutions and opinions.