A frequent schema in my country is to buy votes from local drunks. Go to a local bar with minivan. Grab a bunch of people, drive them to polling station, drive them back, buy beer and give some change.

This doesn't scale that much because you can't verify the vote and you're limited to few days. It's pretty easy to spot it too. Other politics' support is on the lookout for returning cars and scout cheap bars too.

Now move this schema to postal voting. You've plenty of time to buy voting ballots off drunks. And you can fill them in yourself. It's much harder to spot too.

The problem at scale is that you no longer have a secret ballot.

Where I live there are nested envelopes. The outside envelope is associated with you, but the inner envelope that has your vote is not. So they can see that you voted, but not how you voted.

Reading how last US presidential election was caught... You could get hold of someone else's ballot. No need to show your ID to cast in your vote.

That only works if the real voter doesn’t show up.

Given the usual turnout, there's a pretty good chance...