I don't really understand why people care about things like this. Maybe I was a bit too proud to beg, but I never asked for a grade change. Well, I once pointed out a clerical error in summing up answers in a test, but I don't think that counts.
In some courses, I even deliberately gave up points. This was often in courses where homework was a lot of busy work but a low percentage of the final grade, say 10-15%, and the final grade was determined on a class curve. I would learn the material, but skip turning in most of the homework, and planned to do well on the tests.
On the other hand, depending on how the tests and graded materials were designed, there is no reason that grade cutoffs need to be exactly 90%, 80%, 70%, etc. A 50% on a hard (or time restricted) test might be equivalent to a 100% on an easier test that covers the same material. I remember taking difficult college course where I was getting 60s on all the tests, but ended up with As or Bs.