Clarke-Groves: Allocation of a Public Good

Three or more players have to tell the government how much monetary gain a certain option (A or B) would bring them. The government collects these numbers (votes) and chooses the one whose sum of all monetary gains is the largest.
To avoid the obvious temptation to cheat, the government asks for some "taxes" according to the following rule: Consider Player Beth. If the result for the vote would have been the same without Beth's votes, then she doesn't have to pay any taxes. Otherwise, if her vote was substantial, she has to pay the difference between the sum of votes which existed without Beth's votes.