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<p>Indeed. Being exceedingly nice and polite is also good protection in case the Professor decides to grade punitively regardless. This will increase the odds OP can appeal this grade to the department chair or academic dean so an arrangement such as having another Professor from the department grade it. </p>
<p>If the OP is in a situation where the grade dispute needs to be escalated, this would also help future students as if there’s an established pattern of a Professor grading punitively in situations where the student presents a polite good-faith case for a regrade, they can be alerted to put measures in place to ensure it doesn’t negatively impact the student concerned or future students.</p>