Here's another theory: If I'm outsourcing part of a project, I will provide a specification for the work including any constraints I require, you will submit a proposal including estimates of how much it will cost and how long it will take, and I will consider your proposal and decide whether to accept it. You will be available at reasonable times for me to communicate with you, you will provide regular updates as the project progresses, and you will inform me immediately if your estimates are going to be incorrect, or I will not pay you. This is what is known in the business world as "how things actually work if you're the one providing the service and the other guy is the one paying the bills". Final hint: if you don't like being asked for a ballpark figure because it's hard for you to give one, then you were right about one of us being a beginner, but you have misjudged which of us it is.
(Edit: I would agree that co-operative discussions and effective communication are the best way forward in most business relationships. I just think the ideas in this particular article are so obviously one-sided in favour of the designer that no serious client is likely to employ the designer's services on that basis, so they aren't really very useful at all.)