Worth mentioning that ballot stuffing is a problem with the people counting the votes/running the polls, not the voters. So it would be more accurate to say that the problem is preventing the entity that organizes the vote from accessing discrete votes.
The main problem is guaranteeing one vote per eligible voter.
Coercion is a related but smaller problem. It's much harder to coerce most of the people most of the time than it is to stuff the ballot.