An engineer couldn't find a job, so he opened a clinic and put a sign outside that said, "Get treatment for $50; if not cured, get back $100."

A doctor thought that was a good opportunity to show up the engineer and earn a quick $100, so he visited the clinic.

Doctor: I have lost my sense of taste.

Engineer: Nurse, bring the medicine from Box #22 and place three drops in the patient's mouth.

Doctor, spitting out the medicine: This isn't medicine, it's gasoline!

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

The doctor got annoyed and, several days later, returned to recover his money.

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

Engineer: Nurse, bring medicine from Box #22 and put three drops in the patient's mouth.

Doctor: That medicine is the same as for the sense of taste!

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

The doctor left, but after several days, he angrily returned for one last try.

Doctor: My eyesight has become weak.

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

Doctor: But this is only a $50 bill!.

Engineer: Congratulations, your eyesight has gotten better. That will be $50.