So I emailed the COO, here was his response:
Thanks for reaching out. This issue is a bit of a dilemma for us. The rules are very clear that there is no return on certified material and our concern is that this will be an ongoing issue with you. I am sure you can appreciate that our consignors count on us to follow these rules. I discussed this book with our comic graders who inspected the book in person for me and they all feel the grade is correct. Not sure how we can overcome this issue given your position, but I am open to suggestions. Regards, Paul