Make sure there is a clear and written understanding about what you provide, schedules and process. While you may be flexible with some issues there will be times you need to draw the line so don't make a habit of giving anything away. Be professional a d make sure there is a log of events for reference. They are hiring you because you have a service/product they need. Bulling should not be acceptable which is generally the case when a client is hard to get along with. It's generally better to have multiple low margin clients than one big one, it helps to be able to sleep at night. So make sure you have an exit strategy and hopefully you won't need it.  Been there done it. One guy ruined me and it took 4 years to get going again