The best way to get rid of stains, spots and smears is to remove them as quickly as possible, before they have a chance to bake into the paint. If you have stubborn stains, spots or smears, you will need to wash your car and then use a paint surface prep product that will safely, deep clean the surface and remove the contamination.
There are many environmental contaminants that adhere to your paint so stubbornly that even a high-quality car wash can’t remove them. Usually the best answer is to ‘clay’ your paint after washing, Detailing clay is specifically designed to remove many of these bonded surface contaminants, when used with an appropriate lubricant.