In many a tale about fairies, they are said to be able to glamour worthless things like dead leaves so that they appear to be money. Unwitting shopkeepers will accept this money in trade for goods, only to find later on that the glamour has worn off and they are left with twigs and dirt.
My personal experience with such wights has, however, led me to theorize that something else might have been going on in reality, that inspired these stories. Perhaps, instead of the unfortunate human being tricked into visually hallucinating that they were seeing coins or paper bills when in fact they were holding a few leaves (something that most people would find unlikely if not downright impossible), they were just influenced by the powerful magic of fairy to see those leaves as something valuable. Maybe their brain took it one step further and translated “valuable” into “money” when it relayed that information, maybe not – maybe they knew what it was, but also knew for that moment that it was beautiful and precious.
Many of us, especially those of us who work with land spirits, wights, and especially those creatures that might be termed “gentry,” are familiar with both the feelings of awe that can come about when fully experiencing the numinous wonder of the natural world and the feelings of rapture when in contact with the spirits therein. After having spent many long moments fascinated by the minute details of a curling fern frond, or joyfully clutching some piece of quartz that appeared like a talisman on the path beneath my feet, it is not a far reach to imagine accepting such gifts as payment, momentarily unaware that they could not buy me anything in this world.
Fairy tales are echoes, I think, of real encounters, half-remembered and embellished for the telling. Fantastic stories that seem invented may actually reveal a potent truth, if examined by those experienced in the realm of spirits.