Maybe an anonymous complaints/suggestions procedure would be the way ahead.
I know that when I was a student we would suffer in silence because "if we make a fuss we will be marked" - true or not, that is the impression most students have.
OK, anonymous complaints may not help in some cases (you may actually need to know names in particular examples) and there may be some abuse of the system. However, give people the option to put their names on the form and throw the "spoilt papres" in the bin (or better still, recycle them!).
I guess I shouldn't be offering useful suggestions to the opposition, but student welfare and getting value for money are too important.