Reading a book about Vikings the writer strongly emphasizes how wrong the modern idea of the Vikings is and that they were mostly tradesmen and farmers. Their expeditions were mostly made to explore and collect goods and if they could avoid to contrast and fight other people, they would. This is kind of the opposite idea that people who are not familiar with Vikings have, so where does this misinformation come from? is it a case of bad propaganda made by other people, like christians?
I also read about the accounts of Ibn Fadlan describing his encounters with the Norsemen (which he called Rus is that right?). I read a scene from his journals regarding the funeral of a chief and the killing of a slave girl and another one where he describes how dirty and smelly they were. I had the impression that his accounts were closer to the modern idea that we have about the Vikings rather then the one I read in the aforementioned book. Did the two "groups" developed different habits? or are they exactly the same people and I'm just really confused? Sorry for my English I hope what I'm asking is clear.
Well, for one, víkingar were uniformly raiders and pirates. That's what the name means.
Scandinavians, on the other hand, were merchants and traders and farmers and fishermen. Trade expeditions were often armed, specifically to ward off víkingar, but generally speaking, they weren't offensive in nature, rather defensive.
A lot of the bad rap that the Scandinavians get is from the popularization of things like 'Save us, O Lord, from the Fury of the Northmen' and the Great Heathen Army that invaded proto-England, the raids on Paris, etc. and while that's perfectly fine to lay at the feet of víkingar, to call the entire population of Scandinavia 'vikings' would be like calling the entire population of the USA 'marines.'
As far as ibn Fadlan's account is concerned, you need to remember who is writing the source and where it's coming from. Ibn Fadlan was a courtier and a wealthy man, so foreign traders who are from more humble backgrounds would seem particularly unkempt and dirty to him, but Scandinavians generally bathed with a fairly regular frequency.^1
Hope this helps!
^1 Fun fact! The Icelandic name for Saturday is Laugardag, meaning literally 'pools day,' which in turn comes from the day that Scandinavians would wash, at the minimum.