Steam is currently testing a new system that will allow Steam users the ability trade certain items for real money.

The system is currently in beta testing for TF2 only and will allow players to trade items such as consumables and tools, including paints, keys, and crates. Eligible items will be marked as “Marketable” in your steam inventory. Steam plan to open the system up other games once the beta is complete and has proved successful.

[OPINION] If this seems familiar to anybody it's much like the Real Money Auction House that Blizzard created for Diablo 3, the very system that nearly killed all fun from the game for thousands of players. It's very much a system that can ruin in game economies and seems to promote cheating, botting and account hacking because all these things can make real money for players.

Thankfully Steam have a system in placed that you may only trade if Steam Guard is enabled. One of the requirements for this is that you haven't changed your password in the last 15 days, so at least hacked accounts shouldn't be as much of an issue.

Of course Steam don't offer this service for free, item buyers will have to pay a fee based on the buying price of anywhere from 5% upwards. Currently Steam have set a limit of $200 per item as that is the maximum amount of money any person may have in their Steam wallet.
Both of these figures are subject to change by Steam once the system is up and running.

Thankfully in Diablo 3 the market eventually calmed down after everybody stopped trying to sell every item for $250 and now the pricing seems fair and reasonable, with most items ranging from $2-$20.

The system in theory is a good idea, with people lacking the time to play as much as others being able to keep up in game with good character items for a small price. But with some players willing to do anything make a quick buck, abuse of the system is inevitable.