There's not much in the way of profit to be made on the steam market place. It may be possible to turn a profit buying a selling CSGO items cheap and selling them, IDK. Best to ask in a big trading forum which games to trade items in.

Buying and selling cards is a very slow business both because there's not much market liquidity and because there's a 7-day trade hold on anything you buy. It can often take weeks or months to sell a card, foil or background. And while you're waiting for your item to sell there's a good chance some fool will come along and try to sell the same item for half the price you're offering it at.