So how marketable is your film idea or screenplay? I know so many screenwriters and filmmakers who spend months and sometimes years on an idea that is cool to just themselves. Depending on what you are attempting to achieve with your story, you should always figure out if you idea is marketable or if you have a fighting chance of selling the screenplay or final film.Paul Castro, the writer of the Warner Brothers feature film August Rush (Starring Robin Williams) shares with us his thoughts on how to test and find marketable ideas.