My client is a heat treater and receives components for heat treatment.
on receipt of these components, should he perform receiving inspection and keep records
of thesame.
Moreover, when he returns the heat treated parts to the customer, sometimes he lands into Identiifcation problems of the lot, as he has not made any marks on the components.( because he is not supposed to) The problem arises becuse, the customer gets similar parts heat treated by another sub contractor. How does he overcome this problem?

<<My client is a heat treater and receives components for heat treatment. On receipt of these components, should he perform receiving inspection and keep records of the same.>>

It depends on what the contract/PO says. If it says that he is to perform the service on parts that meet "x" specifications, then me must check the parts first to make sure they meet those specifications If, on the other hand, the PO just says heat treat what we send you, then he just has to make sure that what he receives is what was sent and record the receipt. Yes this info must be recorded in some manner.

<<Moreover, when he returns the heat treated parts to the customer, sometimes he lands into Identiifcation problems of the lot, as he has not made any marks on the components.( because he is not supposed to) The problem arises becuse, the customer gets similar parts heat treated by another sub contractor. How does he overcome this problem?>>

He should mark the boxes by lot and keep lots separate within his facility if it is important and required by PO. Since he is not the customer, he need not worry about their other suppliers. He needs only to worry about keeping track of the lots he receives and processes.

He should work with the customer to further clarify what method would be adventageous for both of them as well as determine what they specifically require.