If we went full Minority Report we would have nothing. We cannot prevent the dishonest from being dishonest. We can only punish the dishonest after the fact. A dishinest person doesn't care about ethics. There are none. They do as they please and do anything to get what they desire. We cannot blanket out a simple binar ly switch of whether it is ethical or not. It is too nuanced. The billionaire that steals an apple os a criminal. The starving man that steals an apple is in dire need of help and cannot be blamed. Would he otherwise be condemned to death?

This is not as extreme, of course, but the same ideas can apply. The person who digs a copy out of the trash and goes "haha! Here's my access pass!" Is just as legitimate as the person who purchases it in my book... With some caveats...

The thing is, once that person throws away or sells their purchased copy, they have sood their access. It is the person who sold that tattered copy that now needs to be sure they have no further copies. If they do, they've now copied for redistribution. Doesn't matter that they're selling the original, they've still essentially stolen a copy by gaining access, making a copy, then revoking access while keeping the copy.

The vast majority will be honest.

Are we so worried about that one person costing an author the $15 they were never going to get from that person anyway that we would hover, paranoid, over the shoulder of every person that would want to follow the rules?

After all, in your scenario, they are buying a damaged, presumably used book... So the money doesn't go back to the author or the publisher anyway. It goes to the original purchaser who is now reselling something not meant for resale and making money off of someone else's work after they have already consumed it. If anything, selling the original after consumption and damage is now the unethical thing. At least the person that bought the ruined copy tried to pay for it! They did not steal it outright, they legitimately purchased a copy that the reseller valued at a lower dollar amount.

The vast majority are people like OP. They just want their own personal use copy. They have every means to make their own personal use copy. If someone else already did it the only ethical "break" perhaps is that they are using the shorter road instead of putting in the effort of copying it themselves.

And those two are not participating in redistribution. Only one would be on technicality because the one who purchased an illegible copy does not have that same ability to make their own copy. There it does become greyer, but only because it is indeed being downloaded from an outside source and is not a perfect copy of the exact book in their hands. They are aiding in someone else's redistribution, but their downloading it doesn't change if it was there or not. It was already redistributed illegally.

They have a full, readable copy and could copy it themselves. Thus, I feel it is ethically ok to download a copy that has already been digitalized since it is essentially a shortcut of something they could do themselves.

The person with an illegible book does not have this same ability and, thus, hits one of those caveats on ownership I was speaking of.

Ownership is becoming muddier by default these days anyway. With streaming, digital distribution and other such things it actually is the access you pay for. If I buy a book on Kindle, i have purchased the right to access that book on any Kindle device or App. I do not own any part of that book, even a physical copy... So if I print it for my own use, that is just... Access. Access that can actually be revoked at any time, unlike a physical copy.

The second I give a copy to someone else I break ethics.