Answer:
The customer has a claim against the mechanic, but it's not a claim that's recognized under Regulation E. There's not a question as to the authorization, amount, accuracy, computation or any of the other facets of the seven-part definition of "error" under secdtion 1005.11(a)(1).
Assuming that a debit card was used to initiate the transaction, there's a possibility that Visa or Mastercard rules provide a vehicle for the customer's dispute to be handled. Check the operational guides of your card network for further information.