Wouldn't the coin itself a factor to this too? Especially if you're not using the same coin to do the same flip on the machine and another factor is the atmosphere of the surrounding area and the hardness of the surface where the coin is going to land, the air resistance is always neglected in theory but in practical application, that's always considered right? And regarding the hardness of the surface, there's also the small grooves if the surface isn't smooth. Am I pedantic over this stuff or those can be considered a factor to the fairness of the flip?
they don't have any affect at all on the randomness apparently. as long as one does the von neuman method it doesn't matter about all of those external factors.
just make sure to keep the conditions identical throughout the entire coin flipping process and don't let any of those factors vary. should be a piece of cake.