im a little confused on your story. you said, as on your way down you gave him 10 QR as payment for washing your car. as the time you came back, he didnt wash your car.

lesson: do not pay in advance. until your satisfied with the service, thats the only time you will pay. do you pay the petrol man (for example 30 bucks) before they load petrol in your car? do you pay for your groceries before you buy them? do you pay for your food before eating in a restaurant?