Fortunately, in most cases the stains are simple to remove with soap and water, so they're almost never permanent. But once you've removed the wallpaper, it's important to either sand the walls down or wash them with sugar soap to avoid paint. Combine the water and fabric softener in a large spray bottle at a concentration of one to one.
DIY remove wallpaper - spray bottle with water & fabric ... (Andrew Robbins)
How To Remove Wallpaper With Fabric Softener Wallpaper