I have only ever been out once and bought back but 1, which in time turned into 2. Both are very good customers, always have them done and pay up.
I had a day where I picked up £150 in work which has grown a lot since then.
You can expect a retention rate of 50% and less.( but if your service is good then you can expect recommendations from the ones you do retain)
If your prices are at the higher end you can expect less.
If there is some good cleaners in the area you can expect less.
If you dont look,talk,act the part you can expect less. As soon as the customer opens the door you have already been judged, overly enthusiastic? forget it. lacking in confidence? forget it. Pushy? forget it.
You need to be very confident, friendly polite and respectful. You dont need the work but you would be happy to serve them if they require a very good window cleaning service.