Professionally cleaned windows really shouldn’t spot if it rains within a few days of the cleaning. Dirt makes your windows dirty, not rain. When the dust from landscapers, tree pollen, exhaust, etc. settles on your windows, rain drops move the dirt around, and after the rain dries the dirt becomes much more visible. However, clean windows remain clean after the rain because once the pure rain water dries there is nothing to obscure your view.