Sorry for the title but don't know how to phrase it exactly.
I once read an article about a period (in France I think but I'm not sure) when the cities were growing and people strted to have issues with rats (I think) that were spreading deseases.
So the authorities decided to pay citizens a sum of money for any dead rat they presented. Thes worked for a period until people figured out they could make lots of money out of this. And so they started raising rats only to kill them later and make the money.
I can't find anything online (don't know what keywords to use) but maybe someone has an ideea on when this happend and where.