C. Civil court
There is no crime committed and this case presents a dispute between two individuals.
Civil court is the place where individual disputes are handled. Often these disputes are economic in nature requiring a legal settlement. In the example in the question, the plaintiff is the customer who believes they were provided poor service and they will be requesting restitution. The defendant is the owner of the business and will have to prove it was not his fault the wiring did not work. The judge will act as a third party to decide on the matter and it will be legal binding.