Hmmm . . . I can't say that that jives with my own anecdotal experiences, @szav. For instance, I picked this book up for $821 last year in an eBay auction with quite a few bidders. The same copy had sold for $1,680 on Heritage during the pandemic.
I've been a fly on the wall for many auctions with similar results. If you focus on the hot books—like the Our Flag that sold for a nutty price recently—then it looks like GA is going up, but most books and titles aren't hot. I don't think that GA is down 50% across the board, but I suspect it's down at least 20 or 30%.