I liked the idea. But perhaps it needs to be tweaked. Getting gaming right is hard. Maybe:

* offer a $100 credit to start off.

* offer more services than just a tweet if successful - for example a very simple feedback widget that shows up.

* charge only for delaying ship dates, but not for changing what is being shipped, or for minor delays (say within a week).

* don't charge if the person accepts public humiliation with a tweet saying "I sucked and did not ship my planned item.".