"substitute one box of votes for another box of votes during transit to the counting station."
Australian and NZ polling stations are also the counting station, normally with observers present from all parties who all sign off on and seal the package of ballots before it's sent to the central station.
Counting is generally completed very quickly at each polling station, unless it's close, in which case everything gets recounted more than the usual 2-3 times.
Incidents of ballot tampering are effectively non-existent. (Voter tampering is another matter)
Biting the hand that feeds IT
