This is actually very difficult to answer at least for me due to the dearth of reliable contemporary sources narrating such a case. TL;DR, I regard three typical aspects of the Scandinavian (Norse) people, namely the exploring, the plundering, and the trading rather as distinct each other in many cases, though in some cases they were overlapping, especially centered on the last one (trading).
I can't deny the existence of 'racial' prejudice against Norse (ex-) raiders among the 9th century Frankish elites, but I'm not sure how extent the commoner also shared such kind of sentiment. As I noted in this question thread, however, at least one of the most valuable contemporary account on the Viking Age Scandinavian derived from the court of King Alfred the Great of Wessex (d. 899) who was famous for defending his kingdom against the Vikings. It means that Alfred took an interview with one of the Norse merchant who came from the same region as the raiders.
On the other hand, to wear two hats (helmets?), to trade with the local people and to plunder at the same time was certainly possible especially depends on the trading goods, but would not have been so realistic in many cases.
To give an example, some scholars argue that slave was the staple trade goods of the Vikings, and one of their purposes to plunder across Europe was indeed to hunt the slave. If we accept this hypothesis, these Vikings might also have engaged in trading the captured slaves as well as in capturing them by themselves. I don't personally take this argument at full value, since the managing cost of a not small scale raiding party (with living slaves) must have been expensive and I doubt whether a small number of randomly hunted slaves could make up such a cost. Otherwise, however, to attack the settlement only with small numbers of crews in merchant ship would usually be just suicidal. So, I suppose Viking slave traders sometimes engaged in such a slave hunt by themselves, but not so often than they assume.
If you're interested in accumulating wealth by slave trade, I'd rather suggest you not to raid and hunt slaves by yourself, but instead to buy slaves in one of the Viking Age port towns where the arriving Norse people and local ones establish regular trade, such as Dublin, York and Rouen. It was well-known that the Irish petty rulers sold their war hostages (together with cattle) in Dublin after their incessant skirmishes with their own Irish neighbors. It is also likely that some Baltic port towns like Wolin and Truso in the early 10th century also functioned as such a slave trade hub between the Scandinavian merchant and the local (probably rulers). Then, selling them either in Iberian Peninsula or in Russia with Islamic merchants would certainly make up for your efforts and investment, but not try to meddle with them by force (there are some accounts of mostly failed attempts of the Rus' to assault Islamic markets, mentioned in Islamic sources).
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