I am looking for a short story about an alien or possibly a robot looking for sources of food. The story was read in a school English comprehension text book in the UK in the early 1980's.
Story is as follows:
A man is running a petrol/gas station and diner in the desert, I assume in the US from the stetting although I cannot explicitly recall if the language used english idioms or american. Unexpectedly the man has a visitor who is either a robot or an alien who informs him he is looking for food to take back to his planet and will pay with diamonds. The owner of the petrol/gas station is given diamonds by the robot/alien and I vividly recall a scene in which the man tests if the diamond is real by scoring the glass top of a pinball machine with the diamond.
The man offers the alien/robot a hamburger or hot dog but it is rejected as being too bad quality. Various other foods are tested and rejected. Accidentally the alien/robot takes a sample of the mans leg and determines human flesh is a good source of food. I recall a discription of the man screaming in pain as a needle samples his leg and determines it is good to eat. At this point the voice of the man's nagging wife or possibly mother can be heard drifting down from the upper story of the building and the story ends with the implication that the man will sell his mother/wife to the alien as food.
Can anyone identify this short story title an author for please?