Most Helpful Guy
It’ll make him look like a good salesman which can lead to pay increases or promotions if it’s available to him.
Of corse it doesn’t guarantee that at all, many employers would love to see the employee do really well but not reward them anything extra for it.
Most Helpful Girl
No, but sometimes restaurants like that have contests between stores (like all the Subways in one region, all of the Paneras in that franchise, etc) to see who can upsell the most of something, and the winning store gets a prize of some sort.
Maybe not though, maybe that's just what he's been trained to do.