At least in Arapahoe County, everything we did was in pairs of republicans and democrats, to ensure that it was a fair election as far as we could. This included seal checking, logging the zero counts, etc. Everything had a paper audit trail for who interacted with what, who signed off on what, and what was going on.
I don't know how it worked when the machines were picked up for counting, but I assume similar measures were in place.
Edit: Also, poll watchers from both parties could observe our methods. Everyone had a vested interest in verifying that no tampering was taking place, even if that didn't include election workers.