I think earning refunds would be interesting if it was a cash out / cash in system that could earn you a chance to swap something, like in store credit. I could see for every 3 mystery gifts you give out you earn 1 refund of a skin / champion of your choice. I think this could be profit increasing for Riot as it promotes gifting to others that always makes people happy and less toxic and more likely to spend money.
It would give people a way to justify that gift they may have been hesitant to send as well as helping to erase buyers remorse on a purchase they made in haste. It's a true win / win / win ..
Riot wins with making more = $$$ than what was lost through refunds.
Person with buyers remorse = $$$ back on something they didn't like as well as others happy with him/her due to giving out gifts.
League community as a whole = Winning as this would be a trickle down effect to promote less toxicity as more people have a better outlook as more random gifts are going out into the pool of players as a whole.