If you are a web designer, chances are you have dealt with more than one difficult customer. These customers agree to a design, but then they request a different color scheme and layout. This adds several hours of your time to the job and creates unneeded stress for you.
Part of the problem is that customers do not know what they want until you create it for them. They may make unreasonable requests because they do not know the time and knowledge you put in the project. After the client makes a change request, they will hesitate when you ask for the money you deserve for making the changes.
To protect yourself, always get half of the total before you start on the project. Ask the client to send you three websites they do like and three they do not like along with a detailed list of what they do and do like. Put in the contract that any changes made after they agree on the mockup will be billed at an hourly rate. Do not give them any files until the contract is paid in full.
From: Top Web Design Schools