Actually I was talking about the top sticker, thus implying that any sufficiently large number of requested refunds will likely see an increase in the bureaucracy required to navigate. (see also: mail-in instant rebates, and those returns that require every styrofoam peanut)
I would hope at a minimum they would require either a return of the serial number sticker or advise him that the number is being voided and must be destroyed; otherwise (as indicated in other comments) it could trivially be resold.