Job work can only be done on behalf of registered persons. Assuming Customers who come over for repair are unregistered (likely scenario), service from Client to Customer shall be treated as repair service only.
In instant case, goods belonging to Customer are given to another vendor by Client - thus question may arise as to what is the relevance of word 'belonging' in definition of job work - Will it mean legal ownership or can cover physical possession also? If answer is limited to former, then such transaction to be treated as repair service only.
If qualified as job work, need to comply with GST ITC 04 as well as E-Way Bill
Kind regards,
Abhishek