As a customer, I would be clear on [...] how they did not fulfill my instructions. However, before demanding a refund, [...] I would list what needs to be corrected and allow them the chance to make [...] corrections.*
In my experience, the only way this issue really ever comes up is where a new customer doesn't understand that there are no free revisions for anything not communicated and requested clearly and specifically in the original order. That's another reason why I won't have those types of conversations by phone, where it's up to both of us to interpret and remember what was (and wasn't) discussed. I use my FAQs to make clear that
objective mistakes on my part (such as answering the wrong prompt or leaving out a requested section) are always free fixes, but that
subjective editorial opinions, (such as how the client might have used space differently or what subtopics he or she might have included) are never free fixes. My regular clients sometimes ask for revisions based on feedback they receive from professors about their submissions, but they fully understand that these are always paid edits if I made no mistake and they simply ask for the price when they communicate their revision requests.
Recently, a regular client indicated that the professor radically changed the guidelines for the whole assignment
after I delivered it and demanded (essentially) entirely different essays for the assignment on the same day that it was originally due by me to the client. The client paid me to write roughly 80% of the project all over again but understood that this kind of thing is caused by the professor and not the fault of the writer. In the past, I've had new clients who did not immediately understand that kind of thing until I explained it. Other times, I've had clients order a simple project for a Composition course and then request a free "revision" a week later, after the professor gave them follow-up assignments to change the original essay by incorporating a new issue from the class discussion or from another reading from the course. In those cases, I actually had to explain that no project includes subsequent "revisions" to include additional requests from professors issued after their submission (or my delivery) of the original project, and that I'm more than happy to continue developing the same project according to weekly additions to the specs, but that each one of those additions must (obviously) be paid for the additional work that it represents.
*Quote edited to meet the word-count limitation of quotes on this forum.