A lot of times the traders and the Vikings (raiders) were the same people. Pillage one town and sell the stuff in another. The dragon heads could be removed when they were trading or entering friendly territory so as not to scare the spirits of the land. When they went Viking they would put them on.
:’) “We screw the other guy and pass the savings on to you!” ;’)
The fact is, the Viking Age resulted from a population rise during the Medieval Warming, a lack of land in the homeland, and a power vacuum after the fall of the Roman Empire in its former western provinces. They followed closely in the wake of the Angles, Saxons, and Jutes — invaders of Britain — struck and settled in Ireland, and spread into the north (Iceland, Greenland) and west (Americas).
The Varangians (eastern Vikings) served as mercenaries (and assassins and whatnot) for the Byzantine Empire. Hardraada served the Byzantines in the capital as well as military fronts like Sicily. His last gig was back home, King of Norway, but died in the Battle of Stamford Bridge, defeated by King Harold II of England, himself a few weeks away from death and overthrow at Senlac/Hastings/Battle.