Harm was caused by the prank performer, so there is a forgery case possibility. Your post proves why a "jury of your peers" is a flawed concept--most people don't know the law, they just have opinions.

A forgery case seems to make sense, but a theft case doesn't (unless for example evidence is retrieved from the poster in the form of stolen potatoes).

As for a jury, I think that perhaps it makes more sense to free a person than to find them guilty.

I think the fraud is against the one who put up the "free potatoes" post. The people picking up the potatoes were innocent, just reacting to a great deal.

Here in the states, IMO, the last thing you ever want to do is go to trial with a jury of your peers. Too many close cases are decided by people who, even though they have the law explained to them, don't grasp the gravity/concept of what the authors of the laws meant. Then, years later, if there's a break in the case, the state could take a very long time to release you, if they ever do. And God help you if you're a minority!