Bratslav and Kamanets are both fortress, only sell Powder there, even then its not very profitable until late game.
Akkerman - Salt
Kyzykerman - Leather
Bakhchisaray - Pottery
Cherkassk - Iron, Dye
Azaq-Kale - Powder
Sich - Dye, Powder
Kiev - Butter
Chernigov - Shag
Krakov - Tools
Warsaw - Beer
The best destinations for selling varies with game and the frequency with which you caravan. Find Ingri and assess prices or talk to the mayor and check each commodity thats available.