My idea.

This happens because there is currently no way to trade safely.  You can use a middle man, but unless the middle man is going to hold the item for 45 days so that you can't revoke the paypal transaction you can still get scammed (and I don't know many people who want to wait over a month for their items).  So to solve that issue I would create an automated middleman.  It would use bitcoins so the payment can't be revoked and it would work as follows.  You create the trade on my site and give the link to the person you want to trade with, creating of the trade could also be automated based on outpost trades and the like.  Once the user has accepted you both confirm that the correct person has accepted your trade (my site would provide info about the other person and a like to their steam profile).  Once you know you are trading the correct item with the correct person (with the correct money) you both accept and bots grab the items.  Once the items are safe with my bots a bitcoin address (provided by the seller) is shown to the buyer and once enough money has been deposited to that address my bot would deliver to the buyer (after it is confirmed).  This appears to solve all of the problems, you don't have to worry about currency conversion as you are using bitcoins, all transactions are irreversible and guaranteed and anyone can then use the exchange of their choice to buy/sell bitcoins for their preferred currency.  There is also no fees other than the bitcoin transaction fees (which are pretty low).  I have already looked at all of the technology and it is quite trivial (although I would have to take a lot of time on security and reliability).  Do you think that this is useable?  And would you use it?  In the future I could add the capability to add a bitcoin balance to your account so you only have to pay fees for adding and removing bitcoins but not for trading, but that is just sugar on top.