Yes this is at a Skoda dealership

Silt under the carpets means deep water. I live part of the year in Thailand where flooding is common in the rainy season. First thing you check for on a used car is signs of flooding. Corrosion of the body is not really the issue - the problem is corrosion of electrical connectors which can give endLess problems, and water getting to low-mounted ECUs and things like heater flap motors.

Silt under the carpets means deep water.

No-one has mentioned silt under carpets, only 'under the car' - which I interpret as underneath. Mechanics don't often look under carpets.

I take your point but I am puzzled where the silt would be under the car. Presumably it wouldn't cling to the flat underbody. Has it collected on top of underbody shields? I think I'd be investigating further and I would look under carpets to see if water had got into passenger compartment.

It may not have been driven through deep water, just parked for most of the time on a building site/quarry etc where there is a huge amount of dust blowing around.

My wife's old job was on an industrial estate where there was a aggregates company at the end of the road. Over the day hundreds of lorries would drive past where she parked blowing fine silty dust all over the road.

There was little point in trying to keep the car clean for appearance as after a day parked there it was filthy again. When I did clean the car every few weeks to try to stop the dust build-up causing mechanical problems, I blasted underneath it with a hosepipe and the driveway was always covered in a thick layer of silt afterwards.