I worked as a poll clerk in a Canadian federal election once and counted ballots and the experience left me with full confidence in the system. It would be impossible to game on a large scale and incredibly difficult on a small scale.

From what I recall, our polling station, which served only a small portion of the city, was broken into several polls, each run by 2 or 3 poll workers.

At then end of the day the poll workers personally counted the ballots they collected at their poll (so every ballot was counted at least twice, and each individual only counted a fraction of the ballots at the station.) Monitors from the different political parties were free to watch the whole process.

I'm definitely getting some details wrong, but generally the whole thing, plus automatic recounts for tight races left no doubts for me.