From the point of view of an academic (who has supervised and marked far too many dissertations and student projects over the years).
In my school, dissertations (first degree or masters) usually include a plan type assignment. Just so you can make sure students actually HAVE a plan, and have something you can give feedback on. Usually of low weight, but high enough that they actually DO it, else you won't realise they're crap at writing (say), until you get the first draft a week before the submission deadline.
In my school, the mark scheme for the plan and for the final dissertation is set by the school, and available to students.
I have seen many students who were excellent at the research write a terrible dissertation. I have also seen students with weaker research write it up really well. The key is LISTENING to your supervisor, although some people, it didn't matter how many times I told then what they needed to do, they still didn't do it.............
You don't appeal marks at uni, usually. As long as things are marked according to the mark scheme (for example, if two marks were assigned to your consideration of ethics, and there was no such mark given, not even saying 0/2, then possibly an appeal because correct process not followed. BUT marker thinks it was only worth 0.5/2, and you disagree? No dice, because as I keep telling students, lecturers ARE the authority when it comes to judging matters within their subject.
As regards final dissertations, usually marked by two people. In my school, the supervisor, and a second marker who also marks a whole bunch of others. And then the two markers have to try and agree a joint mark and explain why blind marks were so divergent (if they were). If they can't agree, then gets passed on further up the chain.
At the end, external examiners mark a selection of dissertations, and some times give advice such as overall, they think our marking scheme is too generous or needs to be adjusted for next year.
And very finally, students are anyway told that they may still get a first, even if their final mark is 68 or somesuch. The rules on exactly how this is decided vary between schools and unis. But it is all down there in the academic regulations on assessment.
Listen to your supervisor, and pay attention to the marking scheme, and do what you are TOLD will get you marks if you want the marks.
Here endeth the rant!