To me, "in" means that to the best of your knowledge and in consideration of current circumstances, you have all the intention of attending the game.
But not all of us have crystal balls. Circumstances do change, despite the fact that your intent has not. Punish the change in intent, but not the change in circumstance.
The questions become:
1) how do you tell the two apart?
2) the host is still left with an attendance issue. How to deal with that?
Pre-pay with no refund? I'm cool with that, but I'm sure I'm the minority here. Most likely, we just have to accept the fact that there will be a certain percentage of flakers for every game and the host just needs to factor that into the price of the game.
I'm definitely not supportive of some sort of "flakers" list or other such witch hunts.