just use a multisig
both sides send a public address to each other
use those addresses to create a 2 of 2 multisig
(if you want 2 multisig addresses(escrows) both sides create 2 public addresses each and share them to create 2 multisigs)
fund the multisig and then when its funded you both have to decide on the destination(s) and amount of the fund(s) which you then both sign for
no middle man needed. just each other being co-signers to make sure it only leaves the multisig when both sides are happy with destination and amount and time to let it be spent
in short you both become your own escrow
There are several trusted escrows in the forum that you could use, what I see unnecessary is to make both transactions and also use the escrow. You could specify what you want to send him $400 for and then get back $900. Normally payments are made in exchange for a good or service, not back and forth like playing games.
Yes of course this situation has a history that I didn't explain here. Also before the second transaction happens, the receiving party has to initiate a conversion process. But because it is not relevant for what we have to do, I didn't mention.