I know that you're an one of the employers, but I think your operation plans as bad as you.
You provide illegal salary to hire your staffs, and then in order to reduce restaurant's labor cost. Therefore you always find some not ideal men, who usually make a lot of troubles in here.
I think that you forgot important thing about human, it's one of the most difficult to control factors.
It's a close relationship between salary and ability, and that decide to be hired staffs' ability.