I agree..some of your best client's will start out a complete mess, but that's half the satisfaction. The only thing I would recommend is that if you are working on a %, to move away from it. Once you send client's the message that you are not worth the "time", it tends to stick with you. I moved from a % years ago and it was a hard lesson with all the messy accounts I took on, my time is valuable and when a practice has a mess on their hands, the last thing they should worry about is your fees, you can't and shouldn't work for free which is what you do when you take on those accounts billing a percentage.