Dispute opened on cards

I sold this as a near mint bundle and according to the buyer the slight bend means they are no longer near mint and can’t be graded, I was under the impression that slight bends due to humidity have nothing to do with the cards condition as it’s based off the corners and surface (which are clean) on top of this I used the photos above which highlight the slight bends can I fight the case or do I just refund the buyer as I can’t really be asked to go back and fourth