Doctor sets up a clinic

A doctor sets up a clinic and advertises that he can fix whatever problem you have for $500; but if he can't fix the problem he will pay you $1000. A man sees his ad and thinks that this is ridiculous, so he tries to exploit the doctor. He goes into the office and says "I can't taste anything". The doctor hums and haws and then tells the nurse to put two drops from vial 22 on the tip of his tongue. So the nurse does this and the man reacts violently and says, spitting "Oh gross! That's gasoline!" To which the doctor replies: "Fantastic! You're cured! That will be $500". The man, undeterred from the last time goes to the doctor again, claiming that he can't remember anything. The doctor thinks a moment and tells the nurse to put two drops from vial 22 on the tip of his tongue. The man reacts before she can leave the room: "Wait! Vial 22? That's gasoline? Why would that help?" To which the doctor replies "Fantastic! You're cured! That will be $500". Irritated the man decides he's going to try one more time. So the man goes into the office wearing a pair of sunglasses and claims that he has gone blind and can't see anything. The doctor thinks a moment and says, I can't help you. Here is $1000. The man looks at the note in his hand and shouts "Hey! This is only $10!" "Fantastic! You're cured!" cried the doctor "That will be $500".