It is possible the car wash would be liable due to the attendent's negligence. The attendent could likelwise be personall liable due to his/her carelessness. It is also possible the car's owner would be liable, for his/her initial negligence in putting the car in reverse. And it is possible each would be partial liable or responsible for the accident. It depends on the precise circumstances. If the damage is more than a few hundred dollars, it would make sense to consult with an attorney; for a few hundred or less dollars, it probably makes the most sense to simply work out payment among the parties.