Two things that come to mind...
1- Are you qualified to polish the aircraft? Polishing an aircraft can lead to damages if left in the hands of people that are not properly qualified, especially if you scuff the leading edge of the wing or other sensitive areas.
2- What happens to you if by bad luck you fall off the aircraft and break a leg or die? Will you be covered?
In our flight department, even our engineers don't do any of the exterior cleaning or interior grooming when the aircraft is at home base. They hire specialists in aircraft cleaning especially for the polishing.