When returning the rental vehicle I was charged a valet fee due to the vehicle being dirty because of the rainy weather in the area

When returning the rental vehicle I was charged a valet fee due to the vehicle being dirty because of the rainy weather in the area. The vehicle was returned in a washable state as requested, the inside of the vehicle was clean and not dirty. Avis charges you hundreds of rands for a valet while they just take the vehicle to their washbay to get washed that doesn't even cost a R100. I will never make use of Avis again, I have notified my insurance as well of this incident.