How about trying this on your leaflets to stand out.
Offer: Win free window cleaning for a year ! Become a customer and get entered into our annual lottery ( or something like that)
Point them to more information on your website where they can enter into this. At this stage you can get them to check a box should you require any marketing data as well what would help you refine your marketing skills ( optional but a good way of collecting information on buying habits)
They also get to look at your great website.
Select a winner then advertise the winner on the website........
Do this every year and show older winners so that people can see you indeed do this every year.
