Students here do not like evaluation that is derived from group effort, at least not on exams or quizzes. No tests were given. Remember we are talking about teachers in the field with no math expertise. They feel they have a better chance of a better grade. Normally 2 out of 5 are group ratio.
Major projects constitute a significant part of the grade in some cases.
Otherwise I do not use group grading. I ask students to grade their fellow group members in the hope of becoming aware of unequal participation. Quizzes have both a group portion and an individual portion Students are very willing to share their thoughts and they also seem to protect those thoughts that are not to be solved in common. I only access group projects and their presentations. Maybe I should try some of the group test strategies latter.