The bug

Librarians can have 2 different trades of the same level of the same enchanted book, but for different prices. This was previously reported as MC-71354, and it was resolved as "Works As Intended" with the explanation "Random does what Random likes." However, that resolution occurred in 2015 and the recent changes to villager trading in 23w31a mean that this will occur much more often than it used to.

To reproduce

Trade with several librarian villagers until all of their trades are unlocked. Observe their trades. Pretty quickly, you will encounter a villager with two trades for the exact same book for different prices.

Expected behavior

There are 2 possibilities, depending on opinion.
Possibility 1
The books offered by a single librarian should either be different enchantments, or different levels of the same enchantment.
Possibility 2
If a librarian villager has two trades for the same level of the same enchantment, both trades should be the same price.

Observed behavior

Identical books can be offered by the same villager for different prices.

Original description

A similar report was made before and it was marked "work as intended" because the villagers' book trades were completely random. Now the trades are not so random and the problem tends to repeat itself several times.