sentences:  The system with folded and stamped ballots has been criticized, because studies show that about 10% of voters fold the ballot the wrong way, exposing rather than hiding their choice.This can lead to suspicions that this "mistake" is sometimes done intentionally in a scheme of electoral fraud.If someone "buys" a vote, the bought voter can "accidentally" reveal his choice to confirm that she or he upheld his or her part of the deal.