When it goes back
A book goes back the same way it came: through the site it was bought from.
Whose rules apply
The return window, the conditions, and the way the money finds its way back are all set by the seller of the listing as they stood at the moment of purchase. That listing and its help pages carry the current terms; nothing on this desk overrides them.
Avoiding the trip back
Most disappointments in this hobby are size and appetite, not defects: an album with fifty rooms lands on a desk that wanted five. The scene counts on our cards and the three question picker exist to catch that before the box ships.
Back to the shelves
The books are the point; the paperwork just keeps the desk tidy.