I don’t know what type of video you produce, or what type of clients you have. But for me, it will take at the very least a meeting with the client to discuss the project and a meeting wth the client and scriptwriter to get the information needed to write a script.
Let’s use a custom home builder as an example. Basically what you suggesting is have an architect design a home for free, create the blueprints and then see if the home buyer will hire him. That’s all backwards.
You’re designing a video program and then trying to get the client to approve it. Again all you should be doing is providing a creative treatment and walking them through the project, explaining how you’ll approach it. You’re jumping ahead of yourself with storyboards and scripts.
If you follow the way I’m suggesting you work, you won’t lose a project based on the fact the client doesn’t like the first script. You’ll work on the script once they hire you, and then you can keep making changes until they are happy. With your techniques, you might as well produce the whole video for them and if they like it they’ll pay. See what I mean?