Somebody else mentioned that some areas have a system where if you show up in person, your mailed ballot is invalidated. That seems like a good safeguard.
The bottom line for me is that I think the option of mailing ballots increases participation. There may be an increased number in coerced ballots as well, but I think the net result is postitive.
Filming yourself could easily be prohibited. In France, I'm pretty sure that the voting officer wouldn't let me put my ballot if I was filming myself doing it.
Canceling mailing or e-voting ballots when voting in person can be countered by requiring that the person hand over his ID card for the vote duration.
The idea that a vote might have been bought is a dangerous one. It's dangerous even if votes buying are not proven. I'm still not convinced about e-voting for this reason. There should be absolutely no doubt on the sincerity of a vote.
Somebody else mentioned that some areas have a system where if you show up in person, your mailed ballot is invalidated. That seems like a good safeguard.
The bottom line for me is that I think the option of mailing ballots increases participation. There may be an increased number in coerced ballots as well, but I think the net result is postitive.