Do clients usually agree to this system? If they're unfamiliar with sw development, it might seem suspicious. I wouldn't be exactly comfortable with a plumber drafting up anything else than a standard work-and-parts contract.
It appears like you haven't got very many incoming links to your site yet. Naturally I'm not an expert on optimizing your site, but I would guess that organic search engine traffic should be a major source for you.
For example, I tried googling "books barack obama has read", and you site didn't show up in the first few pages. If I were you, I'd be more concerned about the search engine ranking than optimizing a facebook fan page.
In short: find out ways to get relevant links pointing to your site.