Suppose you purchase an event item you grinded for (e.g 12th anniversary weapon), but it turns out not to your liking, could there be an option to sell it back, either for the full amount of coins or a partial refund with a deduction? Since recent years event items can't be traded, I think it makes sense to have a refund option. It doesn’t have to be for this event specifically, but maybe something to think about for future ones. If it’s possible, maybe it could just apply to items from the current year/event and not previous ones, depending on what the client allows.
