Voting machine integrity through transparency

Maybe a machine can help a human to cast a correct ballot, but I doubt this would have a
significant influence on the overall vote validity. (If a majority of voters spoil their
ballots, I guess the democratic problem is not only a technical one!)

Concerning people with disabilities, I really have similar doubts. I witnessed such situations
myself as my grand father was blind. As a child I had several opportunities to see him
participate in an election and, well, his pragmatic solution was obvious: he was the one who
chosed who was going to help him cast his ballot. Furthermore, being technically curious
himself, I am pretty sure he would not have trusted the machine more than the person he
designated.
All in all, IMHO, such an example probably reduces to a conventional delegation issue, not
specifically related to disabilities.