I just learned about the warehouse a couple of days ago and tried selling one weapon to see how it works. And while their automated trading system is pretty neat, I cannot understand why anyone would actually use the service considering the prices are not really any good. Giving them 2 weapons will not give you enough credits to buy a scrap... 3 rec will not buy you a ref... You will have to significantly overpay for Bill's or buds (23 keys for the latter). While it's a reliable way to get some odd weapon you might be looking for, I can't imagine any one actually using the site regularly for trading. Am I missing something here?
If I trade in a refined metal, they pay me 4400, while they sell refined for 4500. So I lose 100 "credits" on the deal. I have to trade in 5 refined for that to add up to a scrap. The way I see it, I'm paying them a tiny fee to get precisely what I want immediately, without having to deal with TF2TP or TF2Outpost. I can also quickly dump off a hat that I got in a drop without having to scrounge around to find a good deal in a trade server.
It basically has two uses:
Newbies can trade in a few useless drops to get one that they want. They don't have to rely on finding people to help them out. This isn't quite as useful with GAF because
usually you can find someone to help you if you're specific on what weapon you want.
High-level traders can also drop in a bunch of refined or high-level items and buy whatever they're looking for. Last week I bought 6 hats and 5 strange weapons I was specifically looking for in the span of an hour. That would have taken days in trade servers or on trade sites, unless I was willing to overpay to get an immediate seller.
Unusual-level traders don't usually mess with the place. You can consign unusuals, but you'll only ever find low-tier versions there. The really good stuff still sells on SourceOP.