I can't remember seeing any headlines phrased as questions in any credible German news paper (there's one on 'Sun' level named 'Bild' which I refuse to read, so no comment on that).
There are also some weekly news papers which sometimes contain longer opinion pieces; those might have question marks in their headlines, but usually they aren't too sensationalist.
I often find it interesting to read the headline and then the final paragraph of the article text.
For example headline: "X causes Y" Final paragraph: "No links were found between X and Y"