The standard distance-selling return is a clean loop: the customer changes their mind, sends the item back, you inspect it, and it goes back into stock none the worse. It works because a boxed product is the same product a fortnight later. A plant is not.
By the time a returned plant reaches you it has been packed in the dark, carried on a second courier run, and starved of light and water for days on top of the days it already travelled out. Even a plant that was perfectly healthy when it left can come back stressed, leggy or shedding leaves, and a plant that was the customer's complaint in the first place comes back worse. The item you get is rarely the item you could sell.
There is a legal wrinkle underneath this too. In much of Europe the distance-selling right to cancel carves out goods that are liable to deteriorate or perish quickly, which many living plants are, so the automatic fourteen-day return a customer expects from a jumper may not apply to a fern at all. That does not make the problem go away. It means the trade has had to invent its own answer, because the off-the-shelf one doesn't fit.