I agree. Ballot stuffing should be a capital offense.
The cheater and the cheated are both invited to submit evidence to make the determination more accurate. If the cheater doesn't submit the requested evidence, then an independent judgement will rely mainly on the evidence submitted by the cheated candidate. The cheater does not want that to happen, so generally cooperates.
Once the judgement has been made to the extent of the cheating, a SIXFOLD penalty is extracted and the final vote counts are adjusted accordingly.
Let's say candidate "D" cheats his way to a 10,000 vote win. Official examination of the evidence shows that 3,000 of these votes were fradulent. Volia! 18,000 votes are subtracted and candidate "D" has now lost by 8,000 votes.
The system works amazing well. Let's say same scenario as above but he cheats his way to a 20,000 vote win. Same penalty, but he still wins by only 2,000 votes. He gets the office but, even if allowed to keep it, will spend most of the days apologizing to the constituents for cheating. Instead of circling the wagons for him, the party may even pressure him to resign to remove the stench as happened to that GOP congressional candidate in North Carolina.