You can clean windows on the coast and they can literally be dirty again within hours,a few of them would want them cleaned every month but the majority of them are happy to have them cleaned every 6-8 weeks.
There’s salty glass and then there are windows that are 100 yards from the sea,I do a few this close and the windows are white with salt every time they are cleaned,they get the benefit if you have dry weather for a week or so but if there’s wind and rain like I say dirty again within hours,each visit I do frames and glass and they are happy but most wouldn’t want to shell out every 3-4 weeks.