The listing fee is per listing, not per sale
Etsy charges a small fee each time a listing renews. Treated per sale, it is a fixed cost of having the item up at all - a rounding error on a big order and a real one on a small handmade piece, because the amount does not move with the price.
For a seller renewing one listing per order it is that amount; sellers with multi-quantity listings can divide it across the units a listing actually sells, which is the fairer read of what the fee costs each sale. Either way it is paid before a buyer appears, so it belongs in the cost of the sale even when the listing is old.