This "decentralized trading" idea can only work with digital assets (e.g. blinded Bitcoins...), not fiat money. There is no way to "digitalize" a dollar bill without introducing a third parts (called bank, escrower, gateway, exchange...).
Here is a solution using collateral to build a system for trust-less fiat-btc trading:
https://bitcointalk.org/index.php?topic=462236The bank transfer(s) can be reversed after the BTC are released. Alice Will steal Eve's bank data, send 1k USD to Bob, pocket the BTC and then Eve gets Bob in trouble. This happens often enough on both localbitcoins and bitcoins.de already right now (since that's the exact same system these are operating under).
The bank transfer network is the third party in that scheme and it sucks compared to Ripple for example, since transactions between banks are reversible. It would only work with cash-in-mail and even then you need to trust the postal services.
Also if BTC prices fall more than 10% until the BTC are sold, Bob is better off never releasing the coins. Using this system is like shorting BTC on reversible bank transfers no less. Good luck with that.
I agree, but with the Nash equilibrium solution posted here, you don't need to trust the banking system. You can perfectly send cash money by snail-mail.