Learn more about bitcoin first.

Miners can include any transaction they wish, including one that was never broadcasted to the network. Doesn't matter what sort of crap you do, if I mine I block I can double spend 0conf TXes no matter what, if I mine two blocks in a row I can doublespend 0-1conf TXes no matter what, if I mine 3 blocks in a row I can doublespend 0-2conf TXes no matter what.

Serious merchants will NEVER accept 0 confirm transactions.