"Don't just proof it," I'm told by some of my editing clients. "Tell me which are the best bits and which are the worst bits. If there's anything that should be taken out, let me know. And if there's anything that should be expanded, tell which direction I should go in."
When quoting a price for my services, I always examine the unedited text, note its length and estimate how many hours I'll have to spend on it. Also, I ask the client what exactly he/she wants: basic proofreading, copyediting or full content editing - terms clearly explained in this recent article.
