The procedure that led to this paper was to make a sourcebook of passages dealing with the interplay of business and war from Polybius, Livy, and Caesar, and then to use it to uncover the economic side of Caesar's War Commentaries. The typical economic studies, e.g. Bowman and Wilson, omit the business of war; Ernst Badian deals with Caesar's relationship with the publicani, but not the dealings in wartime; Shatzman and Ferrill both deal with Caesar's private wealth; but none have attempted to uncover the means of its acquisition in the actual War Commentaries. Caesar seems interested in directing our focus away from business matters, but parallel instances from Polybius and Livy often help us understand what is going on.
Ancient warfare, burgeoning field, mostly goes to strategy, heroism, war games, and chess on real battlefields. The ancient historians are not interested in "merchants and baggage" (calones, impedimenta). Brief instances where the calones appear in action have to be plucked out with tweezers. They trail an army on the march, ready to buy the captives en bloc and then sell them elsewhere. Caesar shows them to us mostly when they are a stratagem, when he uses their numbers to make his force seem larger than it is.
In all Latin literature we only see one calo: In Plautus' Captives [98-100], we see a father engaging in the buying and selling of captives. This text defines the trade, a questus inhonestus.
The questus inhonestus makes clear why Caesar minimizes any reference to it. But Plutarch's two paragraphs about Caesar's one year in Spain shows that Caesar knew how to make war in a wild province pay. Caesar into Spain: 860 talents in debt; Caesar out: A wealthy man [Plutarch, Caesar, 11, 12). (Verres' problem was he had provinces at peace!)
Scipio in Spain and Africa had 400 transport ships at his disposal, and in Livy 29, we see them running a shuttle service: in with supplies, out with captives and plunder. Plunder and 8,000 captives were loaded on to his transports and shipped to Sicily. Their return was just in time to take off the plunder from the town of Salaeca, the very day. Here Livy himself offers comment: "It almost looked like second sight, as if they had come on purpose to to pick up a fresh cargo of spoils." [Livy 29.35] With that for lens, we see an even larger scale of syndication and transporters marketing in Caesar's wake: disgusted with the false surrender and counter-attack of of the Aduatuci, he sold them all. The merchants are only in a relative clause. "From those who had bought them (ab eis qui emerant), their number was reported as 53,000." [B. G 2.33] Their false surrender is an apologia for selling them wholesale; Caesar's apparent motivation for datum is to blazon the scope of his military achievement.
However, from both Hannibal at Saguntum, and Scipio in Africa, we see that managing the questus inhonestus was standard procedure after a victory. Hannibal or Scipio, it makes no difference. Procedure is Win, Sell, Plan the next thing. We have Livy 21.21 for Hannibal, Polybius 14.9 for Scipio, and a nameless subordinate clause for Caesar.
And finally, who are ei qui emunt? Who are their security personnel? We probably have the answer in Book Seven, where the allied German cavalry have unsuitable horses, and Caesar commandeers good horses from (a) military tribunes, Roman knights, and veterans. [B.G 7.65]: Eorum adventu, quod minus idoneis equis utebantur, a tribunis militum reliquisque equitibus Romanis atque evocatis equos sumit Germanisque distribuit.
At this point we can realize what the equites and evocati are doing there, and we are equipped to see a priceless irony: the cavalry, equitatus, is German allies while the Roman cavalrymen, equites, are the buyers! And their transport security force? That would be the veterans.