actually the system works by players can get atleast half of the card through gaming and half of it is either buy or trade it if you have duplicates card.

for tf2 need total of 9 cards to craft a badge and maximum can get through gaming is 5 cards.
cs:go total 5, so can get 3. others also the same.

for those who got duplicate cards can do trades here with a bot, it do 1:1 trade with the same game but be sure to check the link for information and how to do the trade. http://steamcommunity.com/id/CardExchange