I charged 1 time of $25 pet fee, no matter how long the guest stay. I performed pest control every time after the guest left if there was ever a pet, and the cleaning time is more than double since we have to get rid of all the pet hairs and smells left on the furnitures. I would rather not to host guest with pets but I sometime accept it if the guest seems responsible.
However, 1 guest told me that a pet fee is not legal if its a service animal. I told her that she is welcome to go to other places, it is my house, my rule, and we usually do not have pets at home and it takes extra cleaning after they leave.