We usually will not hire people with poor grades in their physics classes.
Many of our positions are to be TAs in our tutorial lab. We have two labs, the 105/121 tutorial lab and the 106/123/220 tutorial lab. To work in the 105/121 tutorial lab you must have completed either 105 or 121 and 123. To work in the 106/123/220 tutorial lab you must have completed either 106 (to be a 106 tutor) or 121 and 123 (to be a 123 tutor) or 121, 123 and 220 (to be a 106 or 220 tutor.) In order to be prepared to help your students there is a mandatory weekly meeting where you work out the assigned problems for the week. The prep meeting schedule is shown in this link. You will not be assigned to be a tutor if you cannot attend the prep session for that class according to your online schedule.
In order to work as a lab TA, you must have completed the course with a good grade. For 107 and 108 TAs we prefer students who have completed at least the first two semesters of our lab sequence.
We hire graders for many of our classes. In order to be considered as a grader it is necessary that you have completed the class with a good grade.