It does go both ways, though. I'm a software developer/consultant and am sympathetic to the video but lets look at from the other side.
Most pro level consulting teams work open ended time and materials contracts. There's very good reasons for this, but this definitely gets abused to deliver a project that was never expected to come in on budget. It also exposes the client to the effects of bad management or other incompetence without a lot of redress.
Imagine if you were buying a hamburger and they told you that because they burned the first one you're going to have to pay double.
The hard bargaining can go both ways too. I've included what I considered ridiculous rates in a first draft of a proposal (to give me room to negotiate) only to have them often accepted without a blink. In fact, I'm quite sure not having a standard rate card has been responsible for hundreds of thousands of extra money over the years.
It sounds to me like the creator of the video probably does fixed price bidding, at least in part. In my experience that's never a good idea or worth doing - even if you can manage it OK (extremely unlikely) you end up alienating the customer by having to be so anal about scope creep.
If you have a contract where's the after the fact negotiation come from anyway? Are they really willing to say then sue me?