No, I won't read your manuscript

I met a new writing friend over the weekend (he's a screenwriter) and the conversation turned to how often people ask us to read their works-in-progress, and how it puts us in such an awkward position.  In short–it's a little offensive when someone asks us to read their work gratis because 1) we have our own work to do and 2) most people would never ask another professional to provide their services for free.  Yet, there have been times in my career when friends and relatives have asked me...