That's biased reporting. How does he know he's fake? Maybe he just didn't sell the correct spells to him, or the guy didn't do it right. Maybe they can call him "presumed wizard" or "a sorcerer that doesn't quality check his services often enough". Or they can go to the SOURCE and interview him before they call him a fraud. It could very well be that he gave him perfectly functional spells, and explained to the man carefully how to use them. Then the guy could have mispronounced them or wore them on his arm when they're supposed to go into the anus. We can't hold the wizard to blame for his client's misuse.
He should have just upgraded his hit points to Invulnerability or rolled a c24 for Advanced Stealth and done it at night.