I mean, really. TNT comes to mind as a major improvement tool. But that would gouge out a heck of a lot more than a few eyes. I gave up on being fair long ago. My fellow TAs and I are supervised by the professors, most of whom are interested in, and responsive to, any complaints by any student, however groundless and malicious.
Marxist orthodoxy helps too, at least in the humanities.
Nonplussed is correct that the same grade given, for the same course, at the same University, but in different quarters, does not mean the same level of knowledge gained. This is made even worse if you try to assess the grading across different institutions. As a budding researcher, I believe there could be some inferences made in a study of the 4.0 grading system. The variance might be large, and there would have to be many contingencies, but that is true in many real-life settings. The recent upset over grade inflation was based on a statistical study of the 4.0 grading system, and I don't remember hearing any laughter.