To establish trust, both of us are willing to deposit $900 in BTC into an account, which will be returned to us after the completion of the transactions. How should we proceed? How do we find a trusted intermediary?
If you have BTC knowledge, then you do not need a 'trusted intermediary' or an escrow. You can set up your own 2 of 2 multisig wallet, of which either of you will hold a key to this wallet, whenever a tx is created, and it is fine by the both of you, then you both sign the tx and broadcast it to the network, sending it to the destination address. Take note that you should know what you are doing when setting up a multisig wallet, so you don't make a costly mistake.