This finally hit me why it is wrong. The flipping must be done blindfolded and gloved to avoid a biased flipper that does not like your method.
How can the person have bias? The whole point of tossing coins is that the outcome is completely unpredictable for the person. You do not randomly press keys which would have bias on pressing "j" more often than "+" (example). Just take a coin and flip it using the same initial conditions (e.g. thumb nail touches tails).