If I buy a raw book at a show that is being sold as a 9.6 I get to inspect it and make an assumption of my own. If I make the purchase, most of the time the book comes back at the grade I thought or possibly higher. Sometimes it comes back lower. Regardless of what the final grade is (unless it was trimmed or restored in some fashion) the liability falls on me, unless the book is sold as a "guaranteed" 9.6 or 9.8. Was that the case here?
Other things to factor in.
Was the book dropped shipped to Matt without the owner seeing it? Could the book have received damage while being pressed? If it was submitted again, could it possibly get the 9.6?
Bottom line for me...have the book in hand and before a sale is made and have a clear return policy in place.