If he agreed to send $50 in bitcoin to the other guy's bitcoin address and doesn't do it, the cheater loses his collateral (1% of the trade) because robosats keeps it instead of returning it to him, and robosats also uses the lightning network to return the $50 in escrow to the cheated party. Which means the cheater doesn't gain anything and loses 50 cents (1% of the $50 at stake).