Did the Vikings who terrorized the British Isles, and Western Europe also sell people or did they mostly attack and rob?
Yes, they also enslaved people and used them for work.
So called Thrals.
Since antiquity until some 100+ years ago slavery was pretty common.
E.g. Vikings in Russia (Varjags) took over the whole Russia (the European part) and enslaved all the local population.
That why Slavs (people) got their name, because they were slaves of these Eastern Vikings. The Russian ruling class were basically descendants of those Vikings.
E.g. Ivan the Terrible was direct descendant of the ancient Viking ruler Rurikh (Rus).
In the medieval Europe, the rule was, that it was unethical to enslave fellow Christians, but the pagans were free game.
When Lithuania converted to Christianity around 1400 AD, that was practically the end of Slavery in Europe.