picked over

It's a saying that implies someone, or multiple someones, has already sorted through the books you're looking at.
It's a perceptible lack, a malaise of quality a seasoned book dealer will intuit almost instantly. It is a truism that even the junkiest, least interesting collection of books will harbor a few saleable items in its flesh, grown like pearls in a particularly lackluster oyster. When you don't find them you know something is up.

Of course you keep digging, because even after eager fingers have flensed away the obvious 'good stuff' there is nearly always something worthwhile to be harvested from the carcass. It's a professional challenge, gleaning something useful from a pile of bones, like making stock from a chicken carcass.

I was just sorting through a picked-over buy, scraping the salable dregs from the bottom of the boxes, when I chanced upon this beauty.

It nicely illuminates the lure of this whole tedious business, panning for gold in a river of paper.