In the USA it is common for election work to be run or observed by pairs of majority-party workers: one Democrat and one Republican. So there are multiple pairs

In the USA it is common for election work to be run or observed by pairs of majority-party workers: one Democrat and one Republican. So there are multiple pairs of eyes watching the boxes by people of different parties. This doesn't make funny business impossible but does make it both unlikely and difficult to tamper with on a large scale.