The very fact the question of whether a refund is in order if BOTOX was given without consent argues for a formal written consent for each and every treatment. As crazy as it sounds, if a physician pierces a patient's skin without consent, that could be construed as battery. I would hope the legal system would recognize such a claim for its absurdity but we see settlements for absurd claims every day based on technicalities.
While verbal consent should be adequate there is nothing better in court than a printed consent form with the plaintiff's handwritten signature to answer the question of hwether there was consent. It protects both the patient and the physician. Notice the originator of the question wasn't interested in a malpracticeor battery claim as much as getting something for nothing. It's not like there is a sign posted on the cash register that says, "Your purchase is free if you don't get a receipt."