Welcome to the boards, BmoGreen.
I think it would be more accurate to say you’ve put yourself in a hard place. The book was sold as a CGC 9.8 and that’s what you received. If you are unhappy with the book, it’s not because it hasn’t been graded correctly to CGC’s standards, it’s because the book doesn’t meet your standards. It isn’t defective or “not as described” therefore the seller isn’t obliged to pay return shipping (see eBay guidelines on returning items). As this is just a case of you being unhappy with item, the correct thing to do would be for you to pay the return shipping costs.