Pay a better wage to retain good workers for more consistent work.
The last three weeks we have had great and very thorough service, prior to that we suffered through a worker who did the bare minimum and rushed through the cleaning with poor and incomplete results. The last two people who cleaned for us have a good work ethic and it shows.
The pay setup does not seem to reward those who put effort into the job - I scored a 10 today so the employee gets a bonus because she did a good job. A wise employee who wants to retain a good staff rewards their people as well and does not rely on the average consumer to do that for them.