Ye, the pics do show it in rather good condition, but the inside, especially the floor, ammo racks, rear of the gun etc would defiantly be worn. The area were people climb up and down from the vehicle would be worn, especially along the edges and yes, around the hatch. I did mention this in another thread, so sorry if you read it before, but I drove the same warrior for 6 years, it was never painted, went to Iraq twice, both times having extra armour fitted then removed and probably spent a year of that 6 on exercises, and it wasn't as chipped on the outside as you see some models. And apart from being hit by enemy fire, there's nothing a vehicle in training would not go through that one in combat would.
They do throw up a lot of mud, so you might get the odd chip where a stone may have kit it, but the track guards are quite thin and flexible and absurd most of that. The main thing our use to get covered with from the wheels is mud, which get every where.
One thing to note on the Marder you are doing. Here's a pic which I am sure you have seen. It looks very clean, almost straight out of the factory. But look at the rings on the barrel.
I am a Norfolk man and i glory in being so
On the bench: Airfix 1/72nd Harrier GR.3/Fujimi 1/72nd Ju 87D-3