At first I was not aware if i was doing it right then i caught on after practice to make sure i was
doing it right . The flaw i have found in the trick is that if someone smacks the coin down at an
angle and not straight down on the coin it will mess up the prediction . So while its clever and a
head scratcher if someone comes down on the coin at an angle and not straight on you will actually
predict wrong . I don't know a way around this but if anyone has any advice id love to know because
i do really like the effect. But because to me this wasn't addressed and theres no work around it
loses two stars in my book .
I understand your situation with how the spectator smacks the coin, most the time I just let the coin spin till it stops oppose to smacking action. Just pointing out an alternative, hope this helps.