Finding treasures at used bookstores requires a systematic approach.
I’d recommend visiting those used bookstores you can get to easily at least once a month for a few months. Pay attention to how quickly their classics books turn over. If you see the same books month after month, you can visit that store less regularly. Note that there is some cosmic rule which requires that if a used bookstore has any classics books at all, one of those will always be a student edition of Terence’s Phormio — which will never be purchased. Don’t count that in your census.
Each bookstore will have its own character. Some may be known for purchasing the collections of academics, or will have connections to those who do, which can lead to a self-sustaining, if slow, classics book cycle. There’s one bookstore in Madison I try to visit once a month. While I don’t have as much competition as those who, for purely historical research of course, collect girly mags from the 60s, it is nonetheless true that a beautiful edition of Page’s Poetae Melici Graeci, or a Clementine Vulgate, are once a decade finds, if that. I’d say I visit my main used bookstore four or five times in sequence without buying anything. But then there’ll be a bonanza month, when they’ve just acquired someone’s classics library or got a shipment from some other bookseller who did, when I may walk away with several treasures and only slightly poorer.
I have been to a few used book stores and found used books for more money than I can buy new.
I have to travel too much to visit regularly so I may be missing out on some that cannot be bought new anymore.
Well, at the used bookstores I (used to) haunt, pricing basically worked like this for Classics books - if it was a book that was in print (i.e. Cunliffe, Loebs), they would sell it for cheaper than the new price. If it was an out-of-print book which was in somewhat-poor condition (but still quite readable, otherwise they wouldn’t bother selling it at all - and as long as I can read 'em I’m very lenient towards less than pristine books), it usually fell in the 10-20 dollar range (particularly if it was a slim paperback). If it was out of print and in good condition, it fell in the 20-40 dollar range (particularly if it was a trade). If it was out of print and somewhat famous (like, something written by Bowra) it belonged to the 60-80 dollar range (particularly if it was a hardcover in good condition). I never bought books in the second two categories for financial reasons. Those are also the books which have a slower turnover rate as far as sales. However, I can see how it would be worthwhile for the store to keep those books on the shelves for a while and when they finally do sell them, sell them at a high price.
The two stores I know of which sell new Loebs are Green Apple Books and Borders. Green Apple is probably the most successful used bookstore in San Francisco (they are the ONLY non-chain bookstore I know of which is able to buy enough Harry Potter books to sell it at a discount), so they probably can afford to sell new Loebs on a small margin to entice the Classics types (though I only buy their used Loebs - the price is cheaper and the selection is much better), and Borders just might be able to buy enough of them to get some kind of discount on them.
When I ran a trade bookstore, the pricing on Loeb’s was an ironclad “NET” pricing, which meant that the discount was 10%. Since shipping and all overhead is taken out of that 10% these books were a wash or even a loss (especially when marked down).
Most trade books are acquired in the 40% to 50% discount range (which is why stores discounting “Harry Potter and the Eternal Series” at 40% are losing money).
Believe me, a store that carries Loeb’s and other scholarly editions does so out of a sense of mission. You should cherish them.