The economics of used book sales

Matt G. asks me:

Twice a year the San Francisco Public Library holds a book-sale benefit at which it resells a warehouse’s worth of used books that have been donated. They advertise that +500,000 items are available. Not matter freaking what, every hardcover is $3 and every paperback is $2. The books are loosely organized into “fiction,” “history,” “essay,” etc but beyond that totally unsorted.

1. Among fiction, which is the biggest section and my interest, I noticed an extreme preponderance of middle-tier literary authors. There was practically no James Patterson and Danielle Steele and similarly no DeLillo, no Pynchon, no Roth. But you could have filled a u-haul with any of, in particular, Gore Vidal, Annie Proulx, Tom Wolfe, and some others. Plus an absolutely disproportionate Herman Wouk showing. Why would these be the most donated books in San Francico?
2. Say you had only an hour to spend at this sale but were ready to part with even a couple hundred dollars. How would you strategize sorting through everything, what kinds of things would you be hoping to walk away with? What if you had the same amount of time and $20?

I say the people who bought Pynchon tend to keep him, and the potential donations of the most popular authors are rejected by the library staff, on the grounds that they otherwise would be accepting too many copies and selling them at too low a price.  I, too, have seen plenty of Herman Wouk at Virginia sales, what is up with that? Do they simply not know they ought to reject his titles?

The way to do well at those sales is to arrive with a knowledge of which editions and translations of the classics are the worthwhile ones.  Otherwise, in this age of used copies available on Amazon, I don’t see why attending such sales should be worthwhile.  They can be good for atlases and picture books.  In the old days I used to scour used book sales for copies of Augustus Kelley editions of the economics history of thought classics, do they still turn up?