There doesn't seem to be. They may have a line they don't cross in terms of the expense of the books, but they had the second edition of Robert Burton's "Anatom

There doesn't seem to be. They may have a line they don't cross in terms of the expense of the books, but they had the second edition of Robert Burton's "Anatomy of Melancholy" on the shelf which I imagine auctions for well into 4 figures, so they set the bar fairly high. The oldest book I saw was from around 1520 I believe. Hard to get much older than that given that serving printed books from pre-1500 ("incunabula") are incredibly scarce.