From Team Fortress Wiki
TF2 Warehouse (TF2WH) is a community-made trading site for items in Team Fortress 2. Instead of trading items to other players, TF2WH buys items from players in exchange for credits that may be spent on other items.
TF2 Warehouse gives every item a value in credits and enables players to buy items with credits and sell items for them. All items that are sold on the site are added to the 'central repository' from which they are resold again. This system enables players to purchase and receive items almost immediately if they are available, similar to the Mann Co. Store, and in contrast with conventional trading where the player must locate a seller manually and debate over a price.
To trade items, TF2 Warehouse utilizes a large number of Steam accounts reserved for bot scripts as well as programs to keep track of item locations, trade histories and credits. Trading is implemented through a queuing system and personal "safeword". Once players sign into the site via Steam OpenID and select a "trade" button, they are added to the queue and to await a friend request from one of TF2WH Steam bots. Via Steam Trading, the bot will notify the trader of their safeword and await the user's selection of ready status. If the item(s) is currently not overstocked, the bot will ready and accept the trade along with the trader's prompt.
To purchase items, a user must browse or search through the selection of items the bots currently hold and click the "reserve" button, which reserves a copy of the item for the Steam user. Similar to selling, initiating the purchase requires the user to select "trade" on the bottom of the right column to be placed in the queue. Items are listed on the site in order of their value, and can be filtered based on a custom search, consigned items (such as Unusuals and low craft numbered items), and unaffordable items. If a user reserves multiple items, the algorithm will automatically attempt to select the bot that has all, or the majority of, the user's reserved items, and notify that bot to initiate the trade process. Users are, however, permitted, to reserve a specific instance of an item if there are multiples of that item currently in stock (with a 2.5% credit cost raise, and the overriding of the combination algorithm).
A tier system is in place in Warehouse that requires new users of the site to build their trust with the website. A first-time user of the site is only permitted to trade up to 10 items and/or items up to a combined value of 50,000c. To rank up to the next tier (and be allowed to buy and sell higher valued items), first-time users must trade at least 2 items AND items with combined value over 10,000c. Ranking up on the tier takes place weekly, specifically between Wednesday and Thursday (estimated -8 GMT), and after this period, a user's weekly stats will be reset. As an incentive for users to trade more valuable items, items below 250c are not recorded in the weekly tally.
Pricing and Currency
TF2 Warehouse uses a currency of credits (abbreviated as 'c', e.g. 400c indicates 400 credits) and each item in the game is given a value in credits. Players were given 500 credits once when signing up during beta. The minimum cost for items is 200 credits (and 10 credits for a Mann Co. Supply Crate), with hats starting at 4,500c, and the Unusual quality hats ranging from 250,000 to 3,000,000 credits.
Warehouse Ultimate and WHX
TF2WH has also introduced systems such as Warehouse Ultimate and WHX for loyal users for a nominal, monthly fee. Ultimate allows users faster time in queues for buying and selling, Reduced fees on sales and consignments, the ability to reserve more items and no advertisements. WHX permits the trading of credits between premium subscribed users.
Controversy and Revisions to Functionality
The Warehouse has been under scrutiny due to several unfortunate circumstances in its history.
Overstocking occurs when an item reaches or surpasses the global stock limit set by the site. (In the past, this number has been 50, 70, and even 100, and at the time of this writing is 80.) A TF2WH bot will not accept items users are attempting to sell if the item is overstocked. Unfortunately, because these bots do not update the stock levels in real time, a bot will accept any number of items in a single trade, even if the stock level is one under the limit, as long as it's in one trade. As a result, stock levels can easily be above the stock limit and reach numbers beyond 100% stocked.
With the popularity of TF2WH among the TF2 trading community, many items are at or over the stock limit, especially undesirable items that are not bought back out of stock by other users. Most notoriously, the stock levels of Refined Metal and Keys are widely high and usually overstocked, despite a huge allowance by TF2WH for so-called "currency" items.
Backpack Size Limits
With the October 9, 2012 Patch, Valve implemented a backpack size limit on unorganized backpack items. Before this patch, the bots were able to contain thousands of items each through the use of a mechanic that allowed new items to be stacked up without being entered in the backpack, since the bots don't actually open a TF2 client and organize backpacks. This is an extreme instance of drops collecting in open slots in a player's inventory that's not actually inside the backpack until the finding mechanism is triggered . On the day of this patch, all TF2WH bots whose backpacks were overflowing this limit could not purchase any items. The functionality of Warehouse to allow users to buy and sell items within the same trade was disabled as a result.
Effects of Scammers
After numerous incidents of scammers and Steam account hijackers dumping off stolen goods in exchange for currency items, such as Earbuds, action was taken to curb the site's reputation as a dumping ground for hot items. Implementation of a Trust Tier system occurred after the culmination of many scam reports involving WH and most notably the hijacking of Steam user The Director 's account.
This trust tier system made it so users of the site would have to build "trust" with the site by working to trade items and reach a level to both buy and sell items of higher and higher value.