Easy recurring payments, payment processing, scheduling, job details (customer A gets the whole 9 yards, customer B only needs X, Y and Z), easy customer communication, etc. But I'm not a cleaner so I have no idea if those are worth it.

Give new customer priority to the contractors that have a high in-service retention rate, perhaps. If you have a history of customers who stop using the service after contracting with you, you stop getting customers.