Issues regarding verification of authentic Botox and correct dosage

I heard that when getting Botox, you must make sure to check if it is genuine and the correct dosage.

But when you actually get the procedure done at the hospital...

Is there a way for the patient to verify this?

They use anesthesia and keep your eyes closed... how am I supposed to know if it's genuine or if the correct amount is being administered?

Please let me know if you have any tips.