What about competitions where there is no prior practice? In mind were the competitions at Arcade Expo: The machines are off-limits until a competition begins, and they ran on a three-strikes format, meaning the only people who could've played on it prior were people who helped set up the events. I don't know if they did or not though.
I can say the same goes for the Pokémon Trading Card Game too. I've read the list of rulings for unclear circumstances (it was about 150,000 characters back in 2008; it's probably much bigger now) and I've taken the test to be a judge, which I barely didn't pass, though I didn't really care to be a judge.
There was a lot of crooked activity back during those years when I competed in the competitions too. Players got their friends inducted as judges, and said judges would wander up and down the aisles and report to the competitors between rounds as to what decks everyone was using and sometimes sneaking information about players' hands mid-match. And, of course, they could always rule in favor of the people they knew.
I think I've mentioned this on some other topics, but it's part of why I can't really trust people who work for an event to play in it. Not necessarily the tournament directors, but more the lower-level volunteers who don't necessarily spend the previous night setting everything up.