I agree with declanja. Most times cleaning fee is incorporated into the price of the rental. I would like to say though that maybe they are charging an extra cleaning fee as they have been burned before.
We have a the property cleaned after each guest and laundry sent out etc, (which is included in the rental price).
I've been renting for a few years now and the only time the place has been left really filthy is by Irish people. Leaving their rubbish strewn around the back of the garden instead of prepaid bags provided. Breaking items, writing on the walls (adults not children). Leaving dirty dishes pots all over the house, when a dishwasher is provided. Taking DVD's, books. games home with them (that have been provided to enjoy while you stay not take home).
This is obviously a small minority but I know it discourages some people in the area where our holiday home is from renting to Irish people when they could rent to a German or American Family for slightly less money and have the peace of mind that the guests will leave the property as they find it.