I'm not sure what you are asking. South of them?
Why would traders go to the north? Are you talking about the ships going to Massachusetts to bring sugar and rum?
When the slaves were sold the ships were loaded with sugar and rum. They went north to Boston because that is where the market was. That is where they sold their sugar and rum. That is where the molasses was made.
If I don't understand the question, ask again.
Slaves came from southern regions with respect to the north. A ship traveling from a slave kidnaping area (why, oh God, are we even trying to justify this?) would be at southern latitudes first before reaching northern ones. Why carry a slave destined for the south, up north first? Even if other cargo was going north later on the same ships?
“Them” means the slaves and an ounce of common sense would have told you that was what I meant.
And even if such a circuitous route took place, that does not excuse the South. It could have made itself inhospitable to the business the moment it wanted, and then the middlemen would be left hanging in the wind. The final customer is what makes it all possible.