[wesleychen]

You can solve this easily by always flipping with the same side (doesn’t matter which) facing up for all flips.

[havnagiggle]

There is skill to coin flipping. You'd need to blind the flipper, either physically blindfold or make it so they don't know which result is the positive outcome ahead of time.

[bee_rider]

Or ask the competitors to flip the coin in a manner they doesn’t allow for skill, like put it in a Yahtzee cup and toss from there.

[xp84]

I was imagining spinning the coin with a flick of the finger. That doesn't seem to be gameable to me, but I supposed you'd need to do a lot of flicks to see if flicking the head side or tails side matters. I'd think there's no way a coin can be more likely to spin an odd or even number of times before falling, but weirder things have happened.

[mewpmewp2]

Unless they can also introduce bias using strength/technique of the throw.