This is an issue that can only be addressed on an individual basis. The reality is that many persons that work within the catering environment either leave because the hours are too demanding or they find another job where they earn more money.
One of my policies is that service charge is not included and all gratuities left are shared between staff. Unfortunately, there are many establishments that do not allow this or take a %. By allowing staff to keep all gratuities, it helps to motivate them and times provide a better service!
Do not overwork staff, allow them to keep 100% of gratuities and be flexible to working patterns.