When you write any sort of an instruction, a technical specificaiton or a brief to your colleagues or contractors, you yourself are responsible to ensure that they understand the task. The problem here is you won’t be able to convey the task to these people, even with a super detailed specification, because they won’t read it carefully, even if it is very well written. And if it is short, some important details will be missing, so nothing will be clear.
The ideal way to work with this is when you meet with people who'll do the job, explain everything verbally, and then they write down kind of a document describing their own understanding of the task. Although this is in an ideal situation.
In reality, most colleagues or contractors prefer to first do a shitty job, then realize that they did the wrong thing. Then they do a shitty job again. After that they finally put some effort to figure out what you actually wanted from them. It is usually cheaper or easier for them to make a couple of useless attempts rather than to understand right away what was really required. As long as it’s cheaper for them to do this, it's hardly possible to change their approach.