You ask a very broad question covering so many places and times that no one answer is reasonable, but let's talk about medieval merchants -- of whom we know much more than we do of merchants in antiquity

Medieval merchants traveled familiar routes between intended destinations where they they had friends, and often received correspondence. They would be aware of hostilities and conditions along the route, and in even of the outbreak of hostilities -- or other dangers, like banditry-- they might cancel or delay trips. Sometimes they'd hire armed guards, sometimes they'd travel with a promise of safe conduct written by a notable, sometimes they'd pay bribes.

A captured merchant might pay a ransom, strike a good deal. In the pre-modern world there was often only a thin distinction between trade and piracy. Merchants might be pirates, and pirates might strike what strike you as commercial deals.

Some pirates and captors were more businesslike, some more brutal, but if you were a person thought to have money it was quite likely that your captor would like to get some of that cash. Its possible that they'd kill you anyway, but for the ransom business that's actually a minus-- hard to get a good price for the next ransom if you acquire a reputation for killing your captives.

And when not ransoming captives, belligerents were stealing trade goods, and indeed they were stealing previously stolen trade goods. Merchants were themselves sometimes lying about the losses they'd suffered to their financial partners . . . all in all a very complex picture.

The predicament of five Rochelais merchants, who had chartered a Bayonnais ship to take 200 casks of white wine from Tonnay Charente to Calais, displays another unfortunate circumstance in maritime life. En route, the ship was attacked by Scottish pirates, who killed some of the crew and presumably took the rest captive. Possibly on the way to Scotland, the surviving crew members managed to retake the ship which they brought to Great Yarmouth. However, fortune did not smile on the merchants because at Great Yarmouth, pirates from Norfolk and Suffolk boarded the ship and took the wine. However, this account of events could also be a Bayonnais cover-up for a defrauding action of their own against the Rochelais. Indeed, cases like these demonstrate the problems of identifying exactly what had happened in the reported complaints over piracy.

​

​

Just a few of the many books treating this subject:

Geza David and Pal Fodor, eds., Ransom Slavery along the Ottoman Borders (Leiden: Brill, 2007)

Jarbel Rodriguez, "Captives and Their Saviors in the Medieval Crown of Aragon" (Washington, Catholic Univ. Press, 2007); Yvonne Friedman, "Encounter Between Enemies: Captivity and Ransom in the Latin Kingdom of Jerusalem" (Leiden)

“THE ANATOMY OF MEDIEVAL PIRACY.” Ports, Piracy and Maritime War: Piracy in the English Channel and the Atlantic, c. 1280-c. 1330, by Thomas K. Heebøll-Holm, vol. 15, Brill, LEIDEN; BOSTON, 2013, pp. 33–54.