This is a thought provoking thread and I appreciate all the comprehensive views, expressed rationales, and Kav admonitions.
Sorry if already addressed but would a reasonable seller-disclosed return period play into any seller responsibility for unknown (to seller) damage hidden within a slab? If an X-Men #1 isn’t actually an X-Men #1 by virtue of 2 missing pages, it would seem that such a factual discovery should be knowable upon receipt and inspection. Further, it would seem that after some period of time buyer acceptance should be deemed to occur (whether or not book is cracked out) and the transaction be viewed as closed?
But things are not always as they seem and I am not an attorney. These questions are meant to be general and not directed at OP’s specific facts.