Isn’t it weird that Jorah sold slaves at Bear Island? Wouldn’t Essosi ships stick to Lannisport at most, with only Westerosi ones going as far as Bear Island? It seems like an even worse trip than, say, Cairo to the Orkneys.

It’s a bit out of the way, but trading happens in the Riverlands (Seagard), the Iron Islands (plenty of foreign ships in Pyke buying stolen goods), and the North as well (hence Barrowton). 

Also, my headcanon is that, since Jorah Mormont was buying luxury goods on consignment, he probably sold the slaves directly to the merchants who were bringing the luxury goods to Bear Island.