Well, I'm thinking more along the lines of Italki. The app would just be for escrow and connecting people.

Someone posts a trash bounty for their neighborhood. Another person accepts the bounty. They exchange messages, the acceptance criteria is agreed upon, and the transaction is completed after the bounty poster has verified the trash is gone.

I think such an app would work great for cleaning up public places, but would break down as soon as people started tried to turn it into a career.