this video will show how to refund Unused taxes of a ticket
in case if there's a ticket which is non refundable, or a ticket which is partially non-refundable, or in some conditions non refundable like case of no-show etc. still you can refund the taxes.
but before process to refund the taxes please check penalties and rules, and also confirm with airline either they allow to refund taxes or do not.
in a time when online travel agencies killing offline agents, it's important to get the customer loyalty in efforts a travel agent must offer their unused tax refund (if applicable) which will give you the loyalty of customer.