Pay by the hour at the rate of $45 per hour. I am very scrupulous, so don't worry about such an honor system, as I am accustomed to reading texts over again even when I think they are done, and as a result, I usually spend longer reviewing them than the actual number of hours I bill.
The number of pages completed in an hour will vary significantly. If I am working from an author's already-refined and edited manuscript I could get through 4 pages in an hour, but if I am working from transcripts of talks, with the writings or talks a non-native speaker of English, or with writing that is not yet edited, I may only complete 1-2 pages per hour.
Clearly stated expectations. There is a continuum between editing and ghostwriting, and I can give you what you want but only if lines of communication and feedback are open, so I expect frequent comments on work delivered for review so as to hone my work for you.