Basically review system is very effective one to maintain high quality.
Not only review system, we are adopting insurance plan for our customers and cleaners. That is also attractive point for high experienced freelancer cleaners.
We believe there are plenty of ways to keep our customers happy.
Uber has a review system, yet lots of stories about low quality drivers. They may be low in overall % of rides but get lots of new coverage overtime somebody has an axe to grind. I think you need to consider this more carefully.