If you would order an esrog for succos, (or a Christmas tree for the holidays) and the seller had issues and couldn't ship your order until the week after YT, would you think that canceling the order is unethical? What would you think of a seller that refuses to refund you, because you had an agreement and the unforseen circumstances aren't his fault? How noble would you consider it if the buyer has pity on the seller, understands that he already put in the effort to fulfilling the order and had issues come up due to no fault of his own, and agrees to buy the items at a loss?
...עברה זמנו, בטלה קרבנו