The City of Brass's price of converting a Wish diamond to a Wish should collapse to a small service charge, about what you'd pay for a few minutes of a noble Efreet's time for any other service; modulo transaction costs that both parties are incentivized to keep small.

(At least, assuming there's no such thing as a 'premium Wish', like one with favorable interpretation, and a verifiable way to offer that service.)

The City of Brass's price of converting a Wish diamond to a Wish should collapse to a small service charge, about what you'd pay for a few minutes of a noble Efreet's time for any other service; modulo transaction costs that both parties are incentivized to keep small.

(At least, assuming there's no such thing as a 'premium Wish' that fewer noble Efreet can offer.)