"I can cure any kind of disease for 500$. If i fail, you'll get 1000$ back"...

... says a sign on the door of a doctor.

So a guy decides "yeah, i'm going to get those 1000 bucks!"

So he goes in and says "doctor, i lost my sense of taste, cure me!"

The doctor says "sure thing, nurse, go get me the box labeled "22" and give him three drops into his mouth".

The nurse does as she was told, and the patient says "Wtf, that's gasoline, you wanna poison me??"
"well, looks like you got your sense of taste back. that will be 500$". the guy pays angrily, but then decides to come back the next day.

"Doctor, i suffer from memory loss, i can't remember anything, cure me!"

"Sure thing. Nurse, get the box labeled "22" and give this pacient three drops into his mouth."

"wait... the cure is gasoline again???"

"well, looks like you can suddenly remember, don't you? that's 500$, then."

The guy has no other option than to pay, but he's really angry now and decides to try a third time, to get his lost 1000$ back.

"Doctor, i have nearly lost my eyesight, i can only see shapes"

The doctor thought for a while, and then said "well, looks like i cannot cure that, here are 1000$, as promised.", and hands him over 10 bills.

"Wait, that's not 1000$, you gave me 10 1$-bills, you wanna f*ck with me?"

"congratulations! you can see again! that's 500$, then"


Edit: [source](http://cdn.webfail.com/upl/img/076d053aa99/post2.jpg) (roughly translated from german)