Hi Holly, pleased to connect with you here!
This is my first reading of your posts, and it's great because I can relate to this one!
Some years back, I got into the business (hustle) of buying/selling signed and rare books. It worked out quite well because most of the books and writers I'm interested in, while quite obscure at times, develop serious "cult-followings" over time.
Whether fiction or non-fiction, I was always quite confident in my choices.
I used AbeBooks a few times too. But first, I would always check bookfinder.com, which crawls multiple book sites and displays everything available based on price. In my experience, the descriptions of the state of the books was always accurate.
That site lets you specify your search by edition, whether or not the book is signed, etc.
Same principle: buy low, sell high. I had a sealed, signed copy of Chuck Palahniuk's "Fight Club" that I picked up for £20 which sold for just over £120, for example.
But, all business aside, the greatest takeaway from all of that was a signed, excellent condition hardback edition of the 1921 book "Mind in the Making" by historian James Harvey Robinson. That has now become my most treasured possession.
Fortunately, I didn't go through any of the troubles you went through with the buyer who rejected the book upon delivery. That would have driven me nuts!
I look forward to reading more of your posts and interacting where I can. Take care!