IMO of necessity any merchant cult in an ancient setting would become
a smuggler cult upon occasion. Governments don't understand the
importance of commerce at this level of development, so sometimes
they restrict it completely to keep the neighbors' evil influences
out (jeez, this still happens) and if you want your cuban cigars or
your sartar ale then you need to go through a merchant who deals in
goods that traveled under the floorboards of the trader prince's
wagon.
Why use a special smuggler's cult? Why not use a faction of Issaries?
That also makes it much more interesting to roleplay, when the good
guys are doing illegal stuff.