Unlike other attempts at creating a peer-to-peer exchange, P2P Exchange does not rely on a web-of-trust system. How is this possible? The answer is quite simple. I like to call the mechanism that executes the trade a "Trader Bot"
Your proposed trader bot does nothing except error checking before offering a trade.  As an open source client, a malicious party could bypass these checks if desired.

I think you're headed down the wrong path, and should integrate in support for a web of trust.  I know of no other possible solution to the problem of a distributed exchange.