Pre-release reviews is a problem on more than just books too. I wish there were more systems to verify that you've at least bought the book, movie, or the product in general before you can review it.

How can I prove that if I borrowed it from a friend or a library?

A number of copy-protection systems for mid-80's to mid-90's computer games asked that you opened the printed manual that came with the game and go to—e.g.—page 32 and type in the first word of the third paragraph. Doesn't seem that hard to automate doing that for ebooks, these days. After all, Goodreads is owned by Amazon so they have the corpus. Just use chapters instead of pages; that will work across all formats.

I'm not sure that would help with organized brigading campaigns like this. In the Internet age, one person with the book could supply answers to these questions for hundreds of people posting fake reviews with only a nominal investment of time.

If each prompt were unique (and given the number of pages and words in a book, they could be) then no - it wouldn't be a nominal investment of time to answer all of them.

You have to answer a quiz

Goodreads is owned by Amazon, who is incentivized by the pre-release purchases that these reviews drive. They're not going to put a lock on pre-release reviews (nor should they) to solve a trolling/bad actor issue.

Why shouldn't they? I think it's ridiculous to be able to review something which you have not experienced and I don't see a good reason why they should be allowed. The lockout should be until at least one person (ideally more) have experienced the fully released product.

Authors and publishers ship pre-release advance copies to popular reviewers, as part a part of the promotion leading up to launch, like movies do with prescreenings. Goodreads is notorious for having these types of reviewers, in fact, it's one of the carrots that serial reviewers go after.

This book is still in editing, though. It isn't even available as a pre-release review copy at all yet.

I mean, this is assuming that pre-release reviews are from advance copies, not WIP.

It's amazing how I see this problem everywhere, not only with books. On trakt.tv, all movies and shows that are for from being released already have ratings...