I did a house about a month ago and it was the dirtiest, Ive ever seen. I tried everything on one side of the house and it wouldn't work to get the complete stain removed. It was the older type vinyl. It was on a main street through town and the hole house had been covered in dirt probably forever. I called the guy and told him Before I got too far that the stain would probably be permanant, but we were literally spraying the mud off the house. Told him we would do our best, but we can not work miracles. He said it was fine go ahead and finish. Just wanted to make sure before I wasted my time and his.
Although it was clean. The stains were are permanent. I thought the whole job was worthless until I came home and looked at the before and after pics.
These pics don't show how dirty the house really was but you can get the idea..