Bitovagas.

An Engineer could not find a job, so he opens a clinic, and puts a sign outside that says

"Get treatment for $50, If not cured get back $100."

A Doctor thinks this is a good opportunity to show up the Engineer and earn a quick $100.

And so he visits the clinic.

Doctor: I have lost my sense of taste.

Engineer: Nurse , bring the medicine from box No 22 and place 3 drops in the patient's mouth.

Patient (Doctor): Spits out the medicine and says "This is not medicine, it's petroleum".

Engineer: Congratulations. You have your taste back. That will be $50.

Doctor gets annoyed, and returns after several days to recover his money.

Doctor : I have lost my memory and can't remember a thing.

Engineer : Nurse , bring medicine from box No 22 and put 3 drops in the patient's  mouth 

Doctor: "This medicine is for the sense of taste" protests the Doctor.

Engineer : Congratulations, your memory is back, that will be $50

The Doctor leaves, but after several days angrily returns for one last try.

Doctor : My eyesight has become weak.

Engineer : Well I don't have any medicine for that. Take this $100.

Doctor : But this is a $50 note.

Engineer : Congratulations, your eyesight has got better. That will be $50 thank you!