(Note: In a lot of post-Christian folklore, the Trickster figure is referred to as "the Devil". I've kept that for this story.)
One day, the Devil was passing through the farms at harvest-time, when he happened upon a farmer who was so well-to-do that he had three full barns full of grain, all waiting to be offloaded to merchants and sold in the market. As you can imagine, the sight of so much prosperity made the Devil furious, and he immediately resolved to play a trick on the rich farmer.
The next day, when a merchant came with his wagon to buy grain, the farmer discovered that the first silo was full of nothing but the most disgusting manure imaginable. The merchant was much dismayed, and had to be given a drink and sent away with a silver coin to settle his nerves, but the farmer spent the rest of the day going around to all of his neighbors and selling them quantities of the fine fertilizer now in his possession. By the end of the day, he had a tidy profit that more than made up for the expense of having the barn thoroughly cleaned.
The Devil observed this and thought to himself, "ah, my lad, you made a mistake, farmers are earthy folks and not to be deterred by a little pig shit. Now come up with a better plan!"
The next day, the merchant again returned with his wagon, hoping to buy a load of grain for sale in the city. However, when the second granary was opened, it was discovered to contain nothing but thousands of spiders, snakes, scorpions, and other noxious beasts. They burst out in a great wave of biting and scratching and stinging, and it was only luck that the farmer and the merchant managed to make it to the farmhouse before they were overcome and devoured alive. The merchant was obliged to spend the night in the farmhouse, and it was only with a great deal of whiskey and soothing and offers of coin that he was convinced to give over his hysterics.
In the morning, it was discovered that the noxious creatures had all perished, but not before they had eaten up every mosquito, slug, tick, and rabbit for miles around, all the pests and annoyances that plague the farmer's life. So, once again, the farmer pronounced this a good result, and, in fact, he estimated that it might be several years before the local population of pests recovered.
The Devil was terribly frustrated. "Now, lad, you'd better think hard this time and come up with something really useless!"
On the next day, the merchant very timidly approached the farm. This time, instead of accompanying the farmer, he insisted on staying at the house while the farmer went out alone and ascertained that everything was well. When the barn was opened, at first, nothing appeared to be amiss, but then the farmer realized that instead of grain his granary was full to the brim with seeds of every type and description, most of which he couldn't identify. The farmer stood there, scratching his head, and finally, the Devil, unable to stand the suspense, appeared in front of him.
"Hah, I've really got you this time!" said the Devil.
"I take it I have you to thank for this series of transformations, then?" the farmer said.
"Indeed! I made a mistake the first two times, but there's no way you're getting any use out of this!"
"Well, what is it?"
"You mean you don't know? I turned all your valuable grain into seeds that only grow into the most horrible weeds imaginable! Thistles and dandelions and poison ivy! Now, aren't you upset?"
The farmer thought for a moment, and then said, loudly, "But this is terrible! I am undone! Whatever will I do now!" He tore at his hair and beat his breast and cried aloud in a paroxysm of grief. The Devil burst into delighted laughter, did an obscene little dance, and then vanished.
Composing himself and straightening his clothing, the farmer returned to the house, where he found the merchant peeping carefully out of a window. "I'm afraid I don't have any grain to sell you," the farmer said gravely.
"Three whole days without a purchase!" the merchant replied. "This is terrible for my profits."
"Yes, I know, but you won't go back empty-handed today. Instead of grain, I have all sorts of seeds with a variety of medicinal uses for you."
"But that's even better!" cried the merchant.
"I know!" said the farmer, grinning. "It's a good thing for us that devil wasn't too bright!"