The onus is not on the seller to describe the card’s condition, that is why it was graded in the first place. If you disagree with the grade, it is your job to contact PSA.
Just so you know, those who grade with PSA cannot then invoke the “grade guarantee” which would allow PSA to “correct” the grade and give you a refund for the difference. That can only be given to a buyer who had not graded the card themselves.
I would recommend reading this thread.