As a hypothetical, sure, I can see how that makes sense. However, verified purchaser reviews have been a helpful reality for the better part of a decade or so,

As a hypothetical, sure, I can see how that makes sense. However, verified purchaser reviews have been a helpful reality for the better part of a decade or so, across different media and vendors: games, physical goods, Amazon books, electronics, etc. Even though it's an imperfect barrier to review quality, at least it is a barrier versus none, and time and time again retailers who've experimented with it have found it a useful signal. Yes, you'll lose out on the borrowers who fell in love with a title, but they can always spend the $20 to buy that book to review it if they really want to (I've done that for things I loved, just to leave a review). But even if they don't, it's still usually a net win: you lose not just the honest reviewers but the 100x spam that outnumber them. When shopping for low-cost products these days, it's not the individual review that matters anymore, just the aggregate ratings. So it doesn't really matter if a few borrowers don't get to leave their rating, it's still more useful for buyers to cut out the spam. ---------- Maybe a simple compromise is to just allow filtering (and adjust the rating) by "verified purchasers only", so you can see both the unfiltered and filtered scores. I'd just leave out the unverified ones altogether, myself, but others could see the raw scores and reviews if they wanted to.