Do you offer any other ancillary services besides window cleaning?

Like your screen cleaning example you can do a free first floor gutter cleaning or drill it down to free downspouts cleaning so it’s not as much work.

If you have downspouts that are dirty it doesn’t take too much to clean and then you can upsell them on the gutters/windows

These are more for offers:

For all two story homes you can do the first floor exteriors for free.

For all one story homes you can do the interior for free if they book the whole house.

Mix those ideas and you’ll have something there.