I would imagine that anything dealing with Black Magic would be pretty heavily frowned upon in most of the city-states, yet would be quite enticing for say, that Thaumaturge with an insatiable desire for knowledge.
There's also probably a brisk trade in pilfered artifacts from places like Gelmorra, Nym, and even Sil'dah.
Texts dating prior to the start of the Dragonsong War would be immensely valuable, and very, very illegal in Ishgard (whether going into the city-state or out of it). Also, I believe most city states charge tariffs, as Aya pointed out, so smuggling ordinary goods in and out and bypassing customs would be a big money-maker, as well. If I remember correctly, the Arcanist questline deals fairly heavily with that issue, as the Arcanists' Guild serves as the customs office in Limsa Lominsa.
There's also probably a brisk trade in pilfered artifacts from places like Gelmorra, Nym, and even Sil'dah.
Texts dating prior to the start of the Dragonsong War would be immensely valuable, and very, very illegal in Ishgard (whether going into the city-state or out of it). Also, I believe most city states charge tariffs, as Aya pointed out, so smuggling ordinary goods in and out and bypassing customs would be a big money-maker, as well. If I remember correctly, the Arcanist questline deals fairly heavily with that issue, as the Arcanists' Guild serves as the customs office in Limsa Lominsa.