I'm far from being an expert but the leaflet looks OK for the most part. My personal view is that a leaflet should be a minimum of A5 size - but I'm sure people get results with smaller.
The only constructive criticism I would offer is:
1) It is generally better to make statements than pose questions (though there are many exceptions
*).
2) In heading your leaflet "dirty windows?", that's exactly what people think of - dirty windows. The most effective advertising tends to create an image in people's minds - preferably one that will trigger a positive emotion.
However, I feel that the biggest error (if I may call it that) is the omission of a contact address.
*) The best example I can think of in using a question to good effect was a local newspaper ad some years ago. It asked "do you scratch your bottom in the bath?" It was a place that sold bathrooms and also offered a re-enamelling service for old metal baths

. So sometimes, using questions can work very well.