>>314763598The rarity of a foil cards depends on 2 things:
1. The game
2. Your Steam level
>go here: http://steam.tools/cards/>find highest priced card>buy game>get luckyFoil card drops are super rare, and it's almost guaranteed that you will most likely not get one.
However, the higher your steam level is by multiples of 10 (20, 30, 40, 50, etc) the higher your chances of getting Booster Packs, which contains 3 cards each with a chance of being foil.
Booster Packs drop more often if you are logged into steam and play games (or idle).