I've not bothered to dig into this, but with all the hennyclucking going on I decided to look at the scan on HA, and the scratch is blatantly obvious, even before I magnified the image. Immediately my eye was drawn to something wonky in the corner, and sure enough it's the scratch. When I buy a pricey book on HA, I always magnify it and frankly I don't know how you could miss the scratch.
I don't think anyone said "suck it up". Richard's question was specifically, what outcome are you looking for? Let's not add fuel to the fire here. People are already hot here, and with no good reason.
Is HA obligated to reholder the book? Do they make any claim about damage to cases? My guess is there's some 'buyer beware' clause in their bidder contract, I know there is for framed art. If they reholdered every book with a scratch it would be a huge headache and cost. That cost would likely be passed on to the seller, not to mention the delay in listing. Who would put up with that? Not a good business model, and not a no-brainer.
Is the buyer obligated to do their due diligence? If the defect is visible then I don't see what recourse one would have. If this is Clink and there's a back cover defect, that's a different story. But even then, if you're bidding on pricey stuff, probably worth a call first. Bare minimum, magnify the scan.