On proveably fair...

OK, so lets pretend you and I are going to make a wager.  I'll be the house, you can call me money jacker.  that's the name of my casino.

We'll do it in person so it's more legit that way.

Before you bet, I'll write down on a piece of paper what the outcome is.

Here's your piece of paper, now don't look yet, it's in invisible ink and only my special marker will work.

OK, give me your money.

Aww, you lose.   Now look at the paper, here is the marker.  What does it say,  it says.. "You lose" !   

See it's provably fair.

I told you that you were gonna lose, and you did.   Super fair.

Or how about this.   

I have 2 invisible ink pens.   On your paper, if you use 1 pen, it tells you that bets over X will win.   If you use the other pen, it tells you that bets under X will win. 

I decide which pen to give you after you place your bet.

See provably fair.   Your super smart.