I will only ever charge you either a fixed price for a month's work or an hourly rate for my time and knowledge. I won't add charges for small changes that can be done quickly.
We're human beings, not drones. No suits, no pretentious manner, just a hard-working guy who's willing to help.
If something takes a lot less time than initially planned, I'll tell you and the bill will go down. I'll also suggest changes in design where applicable.
If I am working on your project then that's all I will be doing. Your project won't get delayed just because I have other responsibilities.