Hi Nichole,
I don't have an answer in regard to using negative point values. What I used instead was one extra, "Miscellaneous," criterion in my Marking Guide. Depending on the activity, it usually was 5, 10, of 15 points. I used this criterion mostly for just what your describe, "formatting or late submissions," and also used it for those unanticipated mistakes not otherwise covered in the Marking Guide by the other criteria.
I don't have an answer in regard to using negative point values. What I used instead was one extra, "Miscellaneous," criterion in my Marking Guide. Depending on the activity, it usually was 5, 10, of 15 points. I used this criterion mostly for just what your describe, "formatting or late submissions," and also used it for those unanticipated mistakes not otherwise covered in the Marking Guide by the other criteria.