I've considered non-refundable deposits... especially if you're hosting a game on your own property, this seems like a no-brainer. Even if people don't pay up before the game, and drop out, you can put it on their tab: if they want to come to another game, they can pony up the penalty fee before even signing up.
I don't think it's necessary for most games, but if you really beleive the integrity of your game (whether it's a scenario, or a skirmish but someone's fronted money) will be harmed by having dropouts, then force a deposit. $10 or $20 out of a 25 field fee would be enough to coax most people into taking it seriously.
Asking people for a deposit would go alot further than slapping some kind of player rating on people - money talks...
aka the fully recovered airsoft addict formerly known as HonestJohn
Igitur qui desiderat pacem, praeparet bellum.