The Idea Behind It
Steam trading cards are nothing special in and of themselves. They look like a normal trading card with a picture, title, and short explanation about it. Depending on the game, you normally recieve half the amount of cards in the set during gameplay. So, if there are 8 cards in the set, you can recieve up to 4 cards naturally from just playing the game normally. Once you have recieved these, you are now eligable for a booster pack, much like a booster pack for any card game. These contain 3 cards in them, and with the natural and booster pack cards, you never know which ones you will get, whether you will get duplicates, or whether you will get rare foil cards. The system is pretty random, and after you have recieved these cards you have to trade to get the rest of the cards that you are missing for your set. That pretty sums up basic idea behind the trading cards, so lets talk about how you can easily make money off of this.Credit: http://media.pcgamer.com/files/2013/05/steam-trading-cards-610x342.jpg
Selling for Profit
Whenever you earn a steam card, you can go straight to your inventory in the steam menu, click on the card you want to sell, then right below the display for it click sell. It brings up another menu which lists all the different price ranges that this particular card has sold for recently, and a place for you to put the price its listed at and what you will actually get from it, since steam and the developers get a percentage from it. After that you simply wait for someone to buy your card and reap the easy profit!
Of course, these cards only sell for about 0.10 to .18 cents, but for getting free cards just for playing a game and being able to sell them with no actual work or time investment is pretty amazing indeed. Not only that, but you can also sell the foil cards for an even larger profit, ranging from 1.00 USD to 3.00 USD. You can also sell the booster packs themselves for a decent profit, normally around 1.00 to 2.00 USD. In truth, sometimes this is better than opening the booster packs and selling them indavidually, since you could reap more profit by just selling the whole pack.
Instead of just selling the cards, you can also go for the whole set and craft the badge. Doing this nets you XP, which is important for card drops, special emoticons, profile backgrounds, and other small goodies. These items can also be sold on the steam market, and are sometimes worth more than selling indavidual cards and booster packs, depending on the current market for those specific items.
Tips on Getting Most Profit
When it comes to trying to use this system to your advantage and getting the most out of your cards and booster packs, it is wise to do research in whatever category you are looking at. More often than not, selling indavidual cards and booster packs is the quickest and normally most profitable way to make money. Now, you will never make anywhere close to even 50 USD with just this system alone, but for the minimum amount of work and effort it takes, who is complaining about some free money for games?
Some cards are sold at a higher price than others, and this is most notably the case when it comes to the foil cards. Make sure to look at the recently sold prices for whatever card your selling and put it around that, so that someone will be more likely to buy it. Also take into account that selling the emoticons and background can net you more money than selling the indavidual cards. Though its not normally a big difference, you can make a decent amount by doing some research and seeing how to best use your cards.
The way it works with XP and your steam level is that every 10 levels the percentage at which cards drop while you are playing a game goes up. When you first reach level 10, cards drop at a rate of 20% more than they originally did. At level 20 it goes up to 40%, and so on for every 10 levels. This is a nice bonus, and something to work towards if you have a good amount of games.
Another way to make easy money with this system is to flip cards, especially foil cards. The way this works is whenever you see another user sell a card at a very low price compared to all the other cards of that type, you quickly buy it and put it at the regular price with all the others. You can normally get a good payout for doing this, but it is difficult to find those cheap cards that make it worthwhile, since steam takes enough of a percentage out of the transaction that it has to be a good 0.10 cents at least to even be worth it. Steam makes it easy to do this since every card is listed with its lowest current price, so you don't have to look through all the sellers and find the lowest priced one. The best way to go about this if you wanna go this route is to search foil in the marketplace and go through all the different cards and find ones that look unnaturally low for that type.
Other than this, that is the pretty much the extent of selling cards for profit on the steam market. Nothing groundbreaking, but a super nice way to earn a little side cash with nearly no effort at all!