got to be the toughest thing of all to get into, unless you buy a round, letters to managers won't work, and they rarely change window cleaners once they have a regular one.
Hard to get the sort of money you would want too, shop fronts are often only a couple of quid, and most are done every week, so it can be tough to have to travel into town just for a couple of quid.
Once you have a load of them they are worth their weight in gold, which is why it is so hard to get them.
Don't bother writing, walk up through your local town, introduce yourself to the manager, hand him your leaflet and ask to give you a call if their window cleaner lets them down.
Don't try and undercut the opposition, it'll come back and bite you on the a r s e.
If you are a relative window cleaning newbie, it will be tough to get a handhold without a decent track record.
Most window cleaners doing shops have been going a long time.
Best of luck though!
Ian