void onFiatPaymentStarted(ResultHandler resultHandler, ErrorMessageHandler errorMessageHandler) {
   checkNotNull(trade, "trade must not be null");
   checkArgument(trade instanceof BuyerTrade, "Check failed: trade instanceof BuyerTrade");
   checkArgument(
       trade.getDisputeState() == Trade.DisputeState.NONE,
       "Check failed: trade.getDisputeState() == Trade.DisputeState.NONE");
   ((BuyerTrade) trade).onFiatPaymentStarted(resultHandler, errorMessageHandler);
 }
 void onFiatPaymentReceived() {
   checkNotNull(trade, "trade must not be null");
   if (trade instanceof SellerTrade && trade.getDisputeState() == Trade.DisputeState.NONE)
     ((SellerTrade) trade).onFiatPaymentReceived();
 }