My flash technique is all over the place right now, just trying to find my groove. If you're asking about the bathroom picture in particular I had a flash 45 degrees camera left (on a shoot through umbrella) for the cupboards and mirror, to give them a little more definition. In retrospect I should have placed it by the window off the right side of the image so the shadows on the drawers are cast in the correct direction. I also had a flash on the ground aimed at the tub on the right side, with a small diffuser on it to give the tub some depth and exaggerate the light that was coming through the window to the right (that you can just see in the mirror). Combined with a few bracketed ambient shots for the floor to bring out more detail.
As for the window I 100% agree, if I hadn't already delivered that to the client I would change it; and still probably will for my portfolio.
The window is extremely minor and I'm sure a client would never notice! You did extremely well, especially given that you're new to this. I would have never guessed that. One thing I do wonder is how did you get so much detail in the lighting fixture in the bathroom? Is that just on a flashed shot?