In my many years as a full-time freelancer, I've worked hard not to underestimate the value of my work and contribution to a project. Thankfully, my clients have always understood my value as well and I've never had to experience this nickle and diming drama (trauma).
I'm not a taco stand, I can't do $8.50, I don't do tests, I don't roll costs over to the next project, I can't help you out, I can't "do this", I don't need "opportunities" and I won't show you how I made it!
Warning... If you are one of these clients, I'm booked for life with other work.