I have been here 6 years - and am on my 3rd apartment.

Each time I have moved I have cleaned the place and signed over the place myself.

Not once have I been screwed over - although I was charged a little for removal limescale (one of their favourites).

To fill walls: a bit of filler - then tippex on top

Marks on walls: buy the white sponges in migros - a quick wipe over and it is gone.

Then just put aside a day to clean. If you get cleaners (which I have never done) make sure you get ones that guarantee the place will pass the "CLEAN" part.

Damage is down to you to correct.