2011 Mercedes E350 no crank/ no start.

Came to the aid of a used car lot to figure out why this vehicle won't start. They had swapped the Front Sam and it did not help of course. We began testing, they disputed our testing and had me go down a bit of a rabbit hole and had me second guessing myself at first but I was on the trail.
There was water in the driver's floor board and we discovered a huge problem that needs addressed. More follow up checks will be needed but we likely won't be seeing this car again.