Hi Richard
Franchising is a complex area, and I speak from experience (having been a master franchisee). Franchisees rightly expect a huge amount and are not always the kind of people suited to hard outdoor work. Collecting £500 in royalties from an unhappy franchisee can be much harder than collecting £12 from Mrs Smith who's been on holiday for a month. (is it maybe worth adding a card payment page to your excellent website?

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An acquaintance of mine operates a system which may or may not interest you. He hires window cleaners on a self-employed basis, allows them the use of an X-reg Escort van, supplies the equipment, the water (they fill up at his house) and the customers. They pay for fuel. He gives them a round sheet every morning and they go out and do the work. He gives them 50% of the value of the work and keeps 50% for himself. He does no cleaning himself. Your top salesman could do the canvassing for the areas that you want to open and instead of offering a franchise (which is very hard to sell, believe me) you are offering a job and you've got 100 people biting your hand off.
This does still leave the responsibility of canvassing and collections in your hands, but it will be far more profitable per unit than selling franchises.