I believe that "medium signs of use" might indicate the scratches at the front of the robot (where the sensor pad is) since it hits walls. It's good to note that the S8 is pretty good at predicting obstacles, so it hits surfaces way less than other robots. Also, the main cleaning brush might show signs of wear, since it's the first piece you change on the robot after a few cleans.

Regarding the right of withdrawal, I believe that Galaxus offers the same time that they do with new products.

Hope this helps.

To question 1: I think digitec understands "medium signs of use" to mean larger (i.e. in length) scratches, from driving against them, and signs of wear on the brush heads.

Since my device is new, I cannot answer this question.