My old lease was ending recently so I switched over to a new model. In the old car I had a small scratch in the non-visible lower side of the front spoiler. To blame is Thalwil's Outdoor ice-skating rink with those earthy parkings having holes you fall into and hit the stone front street or parking curb.

Anyways in the past when I had small damages such as this one and switched to a new car the small damages were "forgiven". However, this time not ... the dealer asked for an insurance number to fix that little damage in the older car and this wasn't exactly a parking damage but a full casco one because I didn't just left and came back to notice the damage.

Isn't it customary for dealers when you switch to a new car to repair those small damages in the old car and not inconvenience the customer with those extra nasty hidden costs?

I would not call them hidden cost. It's spelled out in the contract that you're supposed to return the car with no damages, yes small wear and tear are usually ignored as you experienced. You can either have insurance pay the repair or pay it yourself. This is why your dealer is asking for an insurance " case number". Either way, someone has got to pay the repair needed.

I guess it depends whether you ask before or after you sign the new lease contract.

Typically the sales or leasing team in a garage have scope on freebies and work to make a deal. But once you've signed you're dealing with admin...