The trouble with window cleaning in basic terms is this, it is ideally suited to a small one or two man operation. When you try to raise the stakes it becomes vastly more complicated and the problems and difficulties grow faster than the money.
Its a bit like digging a hole in sand. Too many variables that you can't control. Personally, I like it at the bottom end, its stress free and pretty easy work for what I get out of it. If I wanted to make millions I would look elsewhere.