You wouldn't have to actually do the deed! The "money" they offer is fictional, so why not fabricate a fictional "hit"? Thousands of fictional stories circulate the internet everyday, and few can be proven or disproven. Make the story interesting or funny, include details for realism, and it will grow exponentially in popularity, taking on a life of it's own! If such a story causes one scammer to think twice, it would be worth it!

(Make sure you've got an alibi, though! Coincidences do happen! )