Here is a thought to consider. In the payment provider chat asked the buyer to open a private chat with in you Bisq2 to confirm order details. This should eliminate the third party.
Really important topic to be aware of
join the conversation! https://github.com/RoboSats/robosats/discussions/1746
Discussion
The Robosats chat is already encrypted and peer-to-peer. Opening an other channel does not stop the scammer from just forwarding any request the seller makes to the real buyer.
If the real owner of the BTC and the person parting with their fiat, had way to confirm the transaction details prior pulling trigger this would prevent the man in the middle scam.
If I'm understanding correctly. Person A (the scammer) accepts the Robosats offer and then immediately opens an Bisq2 offer of the same.
Once the Bisq2 offer is accepted the payment details are forwarded to the Robosats offer. In the End, Person A gets the Bitcoin and the other 2 parties get rugged.
Just seems that this is possible because the two parties have zero chance to communicate prior to committing to the transaction.
So what I'm suggesting is rely on a non-Robosats encrypted p2p chat to confirm the transaction.