Doesn't necessarily have to be weighted either. I'm pretty sure that with practice you can get a repetitious coin flip, at least for the flip into hand. I'm doing it right now and if tails is facing upwards when on my thumb I can get heads after catching and putting it on the back of my hand roughly 7/10 times. With practice I could probably make that more consistent. You're just practicing to perform exactly the same flip with the same number of spins every time, it's definitely doable. You could put a few hundred hours in and become an expert at it.