The worst case is actually if the translator has no idea about the meaning or origin of a name. For example, in Stephen King's novel "Christine", there's a cat named "Captain Beefheart" (named after
the musician, of course). The translator of my German edition (not sure if they fixed it in later ones) obviously did not have a clue about experimental music, and so they literally translated that into "Kapitän Rinderherz".
I'm a bit torn about the translated names in fantasy books. I didn't mind them as a child reading LOTR – even now the German names sound mystical and sometime a bit quaint to me.
I could never bear to read the German versions of the "Song of Ice and Fire" books, though. "Casterlystein" instead of Casterly Rock? "Schnellwasser" for Riverrun? And Theon Greyjoy becoming "Theon Graufreud"? Sorry, it just sounds all wrong to me.