That puzzle needed more clarification. The solution talks about having two padlocks affixed to the same box, but I can't imagine any kind of box that can have 2 padlocks affixed to it unless the box is specifically designed to allow 2 locks.
My point is that the puzzle should be updated to inform the reader that designing the right kind of box is a part of the puzzle:
"Jan and Maria each have plenty of padlocks, but none to which the other has a key. Using only the padlocks, keys, and a custom-designed box, how can Jan get the ring safely into Maria’s hands?"
Without a third party showing sales of padlock boxes with and without space for two or more locks, there's no actual way of being SURE which is more common.
Even if there are ten times as many boxes available that only have space for a single lock, what matters in the case of the puzzle is, a box with space for two or more locks is readily available. Suggesting in the puzzle "by the way the box has space for two locks" really kind of destroys the "puzzle" aspect.
