The message correctly verified the sending address.
Your case seem very interesting. I want to know if I got it right: you sold an order for Avalon ships for 5.16 BTC. The sale included an escrow agent, which happens to be the previous owner of the order. So the buyer sent first the 5.16 BTC to the escrow agent. You sent the details of the order to the buyer. Then the escrow agent sent the 5.16 BTC to the exchange address...
Something is wrong or I did not understand what exactly happened. Did the escrow agent sent to the address used to sign the message?
Could you provide more details, like the address used to sign the message and the "wrong" address? The address used to sign the message is the address which the exchange admitted to be shared?
As much detail you provide about every step in the transaction, much better is to determine the point of failure and who should compensate the loss.