Player-decided rewards

One or more players has control over the process of distributing rewards between several players.

That one or more player controls the process of distributing between several players the rewards for completing, or the penalties for failing, a goal.

Does the game system or players decide on the rewards given out?

What precautionary systems do you have in place to avoid abuse of this mechanic? Player decided-rewards can help provide balance to the system however it can also lead to secret alliances or betrayal between players.