What is the ruling on not paying the car repair amount to the worker who closed his shop and left, and what should I do?

If a person pays another to repair something for a wage, and they do not agree on the wage, then a fair wage (اجر المثل) must be paid. If you are unable to reach the worker or deliver his right to him, then give the fair wage as charity on his behalf. If you later find him, give him the choice between the fair wage or the reward of the charity, with the reward remaining for you.