Where's the profit in trading slaves?

How does one make money in the slave trade? I ask because I'd like to feature some slave markets in my campaign for flavour reasons, but need more information about how slave trading works if I'm to portray them accurately to my players.

I'm not asking about slaving, mind you: I can easily see how capturing someone and selling them as a slave could be profitable. I'm talking about actualy trading in slaves: buying them cheap and selling them dear.

The problem I'm running into is that slaves aren't a commodity, as such: They literally don't appear on the trade commodities tables. It seems they're only ever sold at the same price you'd buy them at, making it practically impossible to trade slaves at a profit - especially since you have to pay an upkeep cost for each of the slaves that you own.

Is the answer simply that the "middleman" slave traders I'm imagining don't exist, and that slavers always sell new slaves directly to whoever is planning to put the slaves to work?

Or is training slaves in new skills the only way to make a profit in the slave trade, making labourers the only kind of slave you'd buy directly from a slaver?

[quote="GMJoe"] How does one make money in the slave trade?  [/quote]

And in the game?

Autarch purposefully left slaves out of the commodity table to avoid upsetting the sensibilities of those who are offended by such matters. Should you wish to have active slave-trading in your campaign world, slaves should have a demand modifier for each market and a market price of (4d4 + DM) x 10%) of market class. Slaves would be available in numbers similar to mercenaries of similar cost.

Ports where slaves are captured nearby would have low demand modifiers while ports where slaves are sold to slave owners would have high demand modifiers. In the historical world, you could set the various cities on the west coast of Africa as -DM markets and the cities on the east coast of the New World as +DM markets, or the cities on the east coast of Africa as -DM markets and the cites on the east coast of India as +DM markets, depending on whether you were modeling the Atlantic or Indian Ocean slave trade.