When I bought the car, this issue was up for discussion and got me a small discount on the price. This is how my front lights looked when I bought them:
As I found out this is a usual issue with my model – the glass just wears off. It is 12 years old after all. However, not all is lost because according to several threads on the web this can be resolved in a DIY. I went to buy some materials for no more than 30€ and started polishing my headlights. Unfortunately, I either did something wrong or I was just missing patience since I didn’t seem to have any success at all (besides damaging some paint at the edges, even though I taped it).
I then went to a shop which advertised headlight restaurations. I paid 150€ and am very satisfied with the result. Took just one day as well (and mainly because they needed to dry over night).