Who gets the voucher?
Adult A buys adult B a t shirt for a birthday.. T shirt is too big. Adult C offers to swap it as they have a day off that week. Adult A and B don't. T shirt is now half price and refund is given in a voucher..
Who gets the voucher?.
Adult A who paid.
Adult B who had the birthday.
Adult C who gave up their time to return it. Albeit they offered.
I have already decided but am I fair in my thinking?