perceptions and reality
Agree with Jerr about there needing to be an appeal processes for exam marking (at a 'reasonable' cost? refunded if appeal successful?).
In more than 15 years of assessing exams and assignments (and having some reviewed on appeal), the students most likely to appeal are usually in the category of "they don't know they don't know". (real-life examples of the Dunning-Kruger effect)
Having said that, I've had students who thought they failed only to get more than 90% !!
regards
layman