What's that service that must be provided to customer when he buys goods or service ?

Gifts

selling service

Customer services is something that will give us loyal customer, so yea CUSTOMER SERVICES needs to be given to customer.

it is the quality of this service

I agree with Mr. Hany Bahgat Abd Albasset Alshoura.

customer services. to ensure that the customer becomes loyal.. after sale services provides satisfaction to the customer and capability of learning organizations mistakes through feedback

expired date of product with honesty