A client says they have a screenplay, sixth draft, that needs editing. You both agree to terms and contract/fee and you receive the material and it's poorly written. All of it. Nothing will work as it is. This is good news and bad news. The good news is this project will keep you busy. You won't necessarily have to write the whole thing over, but you will certainly be reformatting most of it. The kinda bad news is unless you're not under a time crunch and have some time to be with, you'll most likely have to let your client know you might not make the deadline due to the amount of editing the project requires. Unless of course you feel you can tackle that much work quickly, kudos to you! Rock on. But, to really catch every little nook and cranny of the work, more time will be needed.
Another client says they have a resume they'd like your feedback on and editing eye to examine. You accept it and holy cow--now you can see why they may not be landing any jobs! Take a deep breath and approach this project the same as would the example above. You're going to need a bit of time to revamp this thing. Especially if the formatting is off and not meeting today's standards, a little more time is essential. And that's okay. When a client hears, "I can use a bit more time" they understand you're truly needing just that--a bit more time to closely edit and comb the project thoroughly. It means a lot to a client to hear you need more time when you yourself probably have other projects to get to; and or, are working on others concurrently.
Ultimately, it's vital to work closely with clients, especially when the work is creative and both yourself and your client want their project to be perfect! And, in having excellent communications with the client, there's an understanding you both have for one another and can better appreciate what the other is trying to do.
