In my humble opinion your business, like mine is only worth what someone might be willing to pay for it so you could advertise it at a price which you could then negotiate.
Because there is no guarantee that customers would stay with the new owner some would view the customer base as worthless. (Window cleaning rounds may be different - I have no experience here).
Any buyer would want to see accounts,so the annual net profit figure will be the figure of most interest. They would look at the net profit figure in relation to the investment so see if it was worthwhile.
The turnover figure might only be of interest to a new owner if they think they could do better.
You occasionally get people looking for ready-made businesses upon which they can build and in this case profit might be of less importance.
The minimum you would want would be the assets (vehicles, equipment etc) but even then its hard to value second-hand equipment.
You would also need to consider any Company liabilities.
Does the Company have a good name and is it well-known locally?
Aa a starting point, I would sell for the asset-value less liabilities, plus the value of the name(if any), plus a nominal value for existing regular customers, keeeping an eye on the annual net income as a percentage of the amount you are asking for (i.e. is the income greater than they would get if they stuck the asking price in a building society, for instance).
If you get no takers then you are left with selling your vehicles and equipment obviously.
Avoid those firms offering to sell your business for you.