Well, trust is difficult to earn. And it's often advised not to give it to anybody. We don't easily trust. But does an exchange offer a solution to this? From a certain viewpoint, it actually is making it more problematic. It adds another layer of trust. Not only are we required to trust the person we're trading with, we're now also required to trust the exchange itself. So far, it is proven with sufficient evidence that exchanges cannot be trusted however huge they are.
The issue of trust is the strong factor that we struggle with on the P2P level. Yes bitcoin in it decentralized system eliminated this aspect of third party transaction if all things are equal but just that human selfish factor that breeds distrust. But a P2P is quite successful with bitcoin transaction if both parties eliminate that distrust. For example there are some P2P local groups were with or without the third party escrow service, some parties still transact successfully without distrust.