Thanks for your reply.

When you say "quite common", can you say in what context you say so? For instance what canton?

I have never heard that in Vaud nor Geneva so far. My inspection in Lausanne was with zero damages, so I do not have first hand experience, but again, never heard anyone saying "I paid only half of the job because the paint-job was old" or "I paid nothing because the wallpaper was X years old".

In fact I was asking what is the legal basis for such "depreciation" and if that is national or cantonal.