Missing Parts or Pieces

[95intruder]

Guys, a customer bought a watch from me. A Casio D240 (from the 1980's). This item is in 100 % working order. Now they want a refund because the light doesn't work the way they think it should(it is not a back light, it is just a small light on one side or the other). They asked for the refund under the premis of Missing parts or pieces. This watch is 100% there and not missing a thing, **bleep**? Do I have to refund their money and accept the return? If so why? what should I do?