You don't even need a fancy machine. Simple practice with flipping and catching a quarter in a consistent way can get you statistically significant differences

You don't even need a fancy machine. Simple practice with flipping and catching a quarter in a consistent way can get you statistically significant differences from a 50:50 ratio between heads and tails. The important part is that you're catching the flipped coin out of the air, rather than letting it bounce on the ground. The bounce is much less controllable than how high and how quickly you're spinning the coin - the bounce depends not only on the rotational and kinetic energy, but the exact phase angle it lands at, whereas at the end of the catch you only care about how high and quickly you flipped the coin, which can be done consistently enough by hand. And honestly, even if they brought a machine, as long as you allow it to land without interference and call which side you want in the air, it'll end up being fine. They'd have to know which side you'd pick in order to rig it, and that's just as bad as the initial coinflip.